William IV (William Henry; 21 August 1765 – 20 June 1837) was King of the United Kingdom of Great Britain and Ireland and of Hanover from 26 June 1830. William, the third son of George III and younger brother and successor to George IV, was the last king and penultimate monarch of the House of Hanover.

He served in the Royal Navy in his youth and was, both during his reign and afterwards, nicknamed the "Sailor King". He served in North America and the Caribbean, but saw little actual fighting. Since his two older brothers died without leaving legitimate issue, he inherited the throne when he was 64 years old. His reign saw several reforms: the poor law was updated, child labour restricted, slavery abolished in nearly all the British Empire, and the Reform Act 1832 refashioned the British electoral system. Though William did not engage in politics as much as his brother or his father, he was the last monarch to appoint a Prime Minister contrary to the will of Parliament. Through his brother, the Viceroy of Hanover, he granted that kingdom a short-lived liberal constitution. At his death William had no surviving legitimate children, though he was survived by eight of the ten illegitimate children he had by the actress Dorothea Jordan, with whom he cohabited for 20 years. William was succeeded in the United Kingdom by his niece, Victoria, and in Hanover by his brother, Ernest Augustus.

William was born in the early hours of the morning on 21 August 1765 at Buckingham House, the third child and son of King George III and Queen Charlotte. He had two elder brothers, George and Frederick, and was not expected to inherit the Crown. He was baptised in the Great Council Chamber of St James's Palace on 20 September 1765. His godparents were his paternal uncles, the Duke of Gloucester and Prince Henry (later Duke of Cumberland), and his paternal aunt, Princess Augusta, then Hereditary Duchess of Brunswick - Wolfenbüttel. Most of his early life was spent at Richmond and Kew Palace, where he was educated by private tutors.

At the age of thirteen, he joined the Royal Navy as a midshipman, and was present at the Battle of Cape St. Vincent in 1780. His experiences in the navy seem to have been little different from those of other midshipmen (though a tutor accompanied him on board ship) doing his share of the cooking and getting arrested with his shipmates after a drunken brawl on Gibraltar (he was hastily released when his identity became known). He served in New York during the American War of Independence. While the prince was in America, George Washington approved a plot to kidnap him, writing "The spirit of enterprise so conspicuous in your plan for surprising in their quarters and bringing off the Prince William Henry and Admiral Digby merits applause; and you have my authority to make the attempt in any manner, and at such a time, as your judgment may direct. I am fully persuaded, that it is unnecessary to caution you against offering insult or indignity to the persons of the Prince or Admiral..." The plot did not come to fruition; the British heard of it and assigned guards to the prince, who had up till then walked around New York unescorted.

William became a Lieutenant in 1785 and Captain of HMS Pegasus the following year. In late 1786, he was stationed in the West Indies under Horatio Nelson, who wrote of William, "In his professional line, he is superior to two-thirds, I am sure, of the [Naval] list; and in attention to orders, and respect to his superior officer, I hardly know his equal." The two were great friends, and dined together almost nightly. At Nelson's wedding, the prince insisted on giving the bride away. He was given command of the frigate HMS Andromeda in 1788, and was promoted to Rear-Admiral in command of HMS Valiant the following year.

William sought to be made a Duke like his elder brothers, and to receive a similar Parliamentary grant, but his father was reluctant. To put pressure on him, William threatened to run for the House of Commons for the constituency of Totnes in Devon. Appalled at the prospect of his son making his case to the voters, George III created him Duke of Clarence and St Andrews and Earl of Munsteron 16 May 1789, supposedly saying, "I well know it is another vote added to the Opposition." Although he allied himself publicly with the Whigs and his elder brothers (who were known for their conflict with their father), the Prince of Wales and the Duke of York, William's record was inconsistent and, like many politicians of the time, cannot be certainly ascribed to a single party.

The newly created Duke ceased his active service in the Royal Navy in 1790. When the United Kingdom declared war on France in 1793, he was anxious to serve his country and expected a command, but was not given a ship, perhaps at first because he had broken his arm by falling down some stairs drunk, but later because he gave a speech in the House of Lords opposing the war. The following year he spoke in favour of the war, expecting a command after his change of heart. None came. The Admiralty did not even reply to his request. He did not lose hope of being appointed to an active post, but when he was made an admiral in 1798, the rank was purely titular. Despite repeated petitions, he was never given a command throughout the Napoleonic Wars. In 1811, he was appointed to the honorary position of Admiral of the Fleet. In 1813, he came nearest to any actual fighting, when he visited the British troops fighting in the Low Countries. Watching the bombardment of Antwerp from a church steeple, he came under fire. A bullet pierced his coat.

Instead of serving at sea, he spent time in the House of Lords, where he spoke in opposition to the abolition of slavery, which although not legal in the United Kingdom still existed in the British colonies. Freedom would do the slaves little good, he argued. He had travelled widely and, in his eyes, the living standard among freemen in the Highlands and Islands of Scotland was worse than that among slaves in the West Indies. His experience in the West Indies lent gravitas to his position, which was perceived as well-argued and just by some of his contemporaries. Others thought it "shocking that so young a man, under no bias of interest, should be earnest in continuance of the slave trade". In his speech to the House of Lords, the Duke insulted the leading abolitionist, saying "the proponents of the abolition are either fanatics or hypocrites, and in one of those classes I rank Mr. Wilberforce". On other issues he was more liberal, such as supporting moves to abolish penal laws against dissenting Christians. He also opposed efforts to bar those found guilty of adultery from remarriage.

From 1791, the Duke of Clarence lived for 20 years with an Irish actress, Dorothea Bland, better known by her stage name, Mrs. Jordan, the title "Mrs" being assumed at the start of her stage career to explain an inconvenient pregnancy and "Jordan" because she had "crossed the water" from Ireland to Britain. William was part of the first generation to grow to maturity under the Royal Marriages Act 1772, which forbade descendants of George II from marrying unless they obtained the monarch's consent, or, if over the age of 25, giving twelve months' notice to the Privy Council. Several of George III's sons, including William, chose to cohabit with the women they loved, rather than seeking a wife. After all, the younger sons, including William, were not expected to figure in the succession, which was considered secure once the Prince of Wales married and had a daughter, Princess Charlotte.

While William had an eye for the ladies as a young man, he appeared to enjoy the domesticity of his life with Mrs. Jordan. The Duke remarked to a friend, "Mrs. Jordan is a very good creature, very domestic and careful of her children. To be sure she is absurd sometimes and has her humours. But there are such things more or less in all families." The couple, while living quietly, enjoyed entertaining, with Mrs. Jordan writing in late 1809: "We shall have a full and merry house this Christmas, 'tis what the dear Duke delights in." The King, generally somewhat of a prude, was accepting of his son's relationship with the actress (though recommending that he halve her allowance) and in 1797, created William Ranger of Bushy Park, which included a large residence, Bushy House, for William's growing family. William used Bushy as his principal residence until he became King. His London residence, Clarence House, was constructed to the designs of John Nash between 1825 and 1827.

The couple had ten illegitimate children, five sons and five daughters, nine of whom were named for William's siblings, and who were given the surname "FitzClarence". The affair lasted for twenty years before ending in 1811. Mrs. Jordan at least had no doubt as to the reason for the breakup: "Money, money, my good friend, has, I am convinced made HIM at this moment the most wretched of men," adding, "With all his excellent qualities, his domestic virtues, his love for his lovely children, what must he not at this moment suffer?" Mrs. Jordan was given a financial settlement of £4400 (equal to £243,400 today) per year and custody of the daughters, on condition she did not resume the stage. When she did take up her acting career again, to repay debts incurred by her son-in-law (the husband of one of Mrs. Jordan's daughters from a previous relationship), the Duke took custody of the daughters and stopped paying the £1500 (equal to £82,600 today) designated for their maintenance. With her career failing, she fled to France to escape her creditors, and died, impoverished, near Paris in 1816.

Deep in debt, the Duke made multiple attempts towards marrying a wealthy heiress, but his suits were unsuccessful. However, when the Duke's niece, Princess Charlotte, the second in line to the throne, died in childbirth in 1817, the King was left with twelve children, but no legitimate grandchildren. The race was on among the Royal Dukes to marry and produce an heir. William had great advantages in this race — his two older brothers were both childless and estranged from their wives (who were both probably beyond childbearing age) and William was the healthiest of the three. If he lived long enough, he would almost certainly become King, and have the opportunity to sire the next monarch. However, William's first choices to wed either met with the disapproval of the Prince Regent or turned him down. His younger brother, the Duke of Cambridge, was sent to Germany to scout out the available Protestant princesses; he came up with Princess Augusta of Hesse-Cassel, but her father declined the match. Two months later, the Duke of Cambridge married her himself. Eventually, a princess was found who was amicable, home-loving, and was willing to accept, even enthusiastically welcome, William's nine surviving children, several of whom had not yet reached adulthood. At Kew on 11 July 1818, William married Princess Adelaide of Saxe-Meiningen, the daughter of the Duke of Saxe-Meiningen. At 25, Adelaide was half William's age.

The marriage, which lasted almost twenty years until William's death, was a happy one. The new Duchess took both William and his finances in hand. For their first year of marriage, the couple lived in economical fashion in Germany, William's debts were soon on the way to being paid, especially since Parliament had voted him an increased allowance, which he reluctantly accepted after his requests to increase it further were refused. William is not known to have had mistresses. The couple had two short-lived daughters, and Adelaide suffered three miscarriages. Despite this, false rumours that Adelaide was pregnant persisted into William's reign — he dismissed them as "damned stuff". William had another illegitimate son, William, before he met Mrs. Jordan and whose mother is unknown, who drowned off Madagascar in HMS Blenheim in 1807. Caroline von Linsingen, whose father was a general in the Hanoverian infantry, claimed to have had a son, Heinrich, by William in around 1790 but William was not in Hanover at the time that she claims and the story is considered implausible.

William's elder brother, the Prince of Wales, had been Prince Regent since 1811 because of the mental illness of their father, George III. In 1820, the King died, leaving the Crown to the Prince Regent, who became George IV. William was now second in line to the Throne, preceded only by his brother, Frederick, Duke of York. Reformed since his marriage, William walked for hours, ate relatively frugally, and the only drink he imbibed in quantity was barley water flavoured with lemon. Both of his older brothers were unhealthy, and it was considered only a matter of time before he became King. When the Duke of York died in 1827, William, then more than 60 years old, became heir presumptive. Later that year, the incoming Prime Minister, George Canning, appointed William to the office of Lord High Admiral, which had been in commission (that is, exercised by a board rather than by a single individual) since 1709. While in office, the Duke had repeated conflicts with his Council, which was composed of Admiralty officers. Things finally came to a head in 1828 when the Lord High Admiral put to sea with a squadron of ships, leaving no word of where they were going, and remaining away for ten days. The King, through the Prime Minister, by now Arthur Wellesley, 1st Duke of Wellington, requested his resignation; the Duke of Clarence complied. Despite the difficulties which the Duke experienced, he did considerable good as Lord High Admiral. He abolished the cat o' nine tails for most offences other than mutiny; attempted to improve the standard of naval gunnery and he required regular reports of the condition and preparedness of each ship. He commissioned the first steam warship and advocated for more. Holding the office permitted William to make mistakes and learn from them — a process that might have been far more costly had he not learnt before becoming King that he should act only with the advice of his councillors.

William spent the remaining time during his brother's reign in the House of Lords. He supported the Catholic Emancipation Bill against the opposition of his younger brother, the Duke of Cumberland, describing the latter's position on the Bill as "infamous", to the younger Duke's outrage. George IV's health was increasingly bad; it was obvious by early 1830 that he was near death. The King took his leave of his younger brother at the end of May, stating, "God's will be done. I have injured no man. It will all rest on you then." William's genuine affection for his older brother could not mask his rising anticipation that he would soon be King.

When George IV died on 26 June 1830 without surviving legitimate issue, the Duke of Clarence ascended the Throne, aged 64, as William IV, the oldest person ever to assume the British throne. Unlike his extravagant brother, William was unassuming, discouraging pomp and ceremony. In contrast to George IV, who tended to spend most of his time in Windsor Castle, William was known, especially early in his reign, to walk, unaccompanied, through London or Brighton. Until the Reform Crisis eroded his standing, he was very popular among the people, who saw him as more approachable and down-to-earth than his brother.

The King immediately proved himself a conscientious worker. The King's first Prime Minister, the Duke of Wellington, stated that he had done more business with King William in ten minutes than he had with George IV in as many days. Lord Brougham described him as an excellent man of business, asking enough questions to help him understand the matter — whereas George IV feared to ask questions lest he display his ignorance and George III would ask too many and then not wait for a response.

The King did his best to endear himself to the people. Lady Charlotte Williams-Wynn wrote shortly after his accession, "Hitherto the King has been indefatigable in his efforts to make himself popular, and do good natured and amiable things in every possible instance." Noted the diarist Emily Eden, "He is an immense improvement on the last unforgiving animal, who died growling sulkily in his den at Windsor. This man at least wishes to make everybody happy, and everything he has done has been benevolent."

William dismissed his brother's French chefs and German band, replacing them with English ones to public approval. He gave much of George IV's painting collection to the nation, and reduced the royal stud. George IV had begun an extensive (and expensive) renovation of Buckingham Palace; his brother refused to reside there, and twice tried to give the palace away, once to the Army as a barracks, and once to Parliament after the Houses of Parliament burned down in 1834. His informality could be startling: When in residence at the Royal Pavilion in Brighton, King William used to send to the hotels for a list of their guests and invite anyone whom he knew to dinner, urging guests not to "bother about clothes. The Queen does nothing but embroider flowers after dinner."

Upon taking the throne, William did not forget his nine surviving illegitimate children, creating his eldest son Earl of Munster and granting the other children the precedence of a younger son (or daughter) of a marquess. Despite this his children importuned for greater opportunities, disgusting elements of the press which reported that the "impudence and rapacity of the FitzJordans is unexampled". The relationship between William and his sons "was punctuated by a series of savage and, for the King at least, painful quarrels" over money and honours. His daughters, on the other hand, proved an ornament to his court, as, "They are all, you know, pretty and lively, and make society in a way that real princesses could not."

At the time, the death of the monarch required fresh elections and, in the general election of 1830, Wellington's Tories lost ground to the Whigs under Charles Grey, 2nd Earl Grey, though the Tories still had the largest number of seats. With the Tories bitterly divided, Wellington was defeated in the House of Commons in November, and Lord Grey formed a government. Lord Grey pledged to reform the electoral system, which had seen few changes since the fifteenth century. The inequities in the system were great; for example, large towns such as Manchester and Birmingham elected no members (though they were part of county constituencies), while small boroughs — known as rotten or pocket boroughs — such as Old Sarum with just seven voters, elected two members of Parliament each. Often, the rotten boroughs were controlled by great aristocrats, whose nominees were invariably elected by the constituents — who were, most often, their tenants — especially since the secret ballot was not yet used in Parliamentary elections. Landowners who controlled seats were even able to sell them to prospective candidates.

When the House of Commons defeated the First Reform Bill in 1831, Lord Grey's ministry urged William to dissolve Parliament, which would lead to a new general election. At first, William hesitated to exercise his prerogative to dissolve Parliament because elections had just been held the year before and the country was in a state of high excitement which might boil over into violence. He was, however, irritated by the conduct of the Opposition, which announced its intention to move the passage of an Address, or resolution, in the House of Lords, against dissolution. Regarding the Opposition's motion as an attack on his prerogative, and at the urgent request of Lord Grey and his ministers, William IV prepared to go in person to the House of Lords and prorogue Parliament. The monarch's arrival would stop all debate and prevent passage of the Address. When initially told that his horses could not be ready at such short notice, William is supposed to have said, "Then I will go in a hackney cab!" Coach and horses were assembled quickly and William immediately proceeded to Parliament. Said The Times of the scene before William's arrival, "It is utterly impossible to describe the scene ... The violent tones and gestures of noble Lords ... astonished the spectators, and affected the ladies who were present with visible alarm." Lord Londonderry brandished a whip, threatening to thrash the Government supporters, and was held back by four of his colleagues. William hastily put on the crown, entered the Chamber, and dissolved Parliament. This forced new elections for the House of Commons, which yielded a great victory for the reformers. But although the House of Commons was clearly in favour of parliamentary reform, the House of Lords remained implacably opposed to it.

The crisis saw a brief interlude for the celebration of the King's Coronation on 8 September 1831. At first, the King wished to dispense with the coronation entirely, feeling that his wearing the crown while proroguing Parliament answered any need. He was persuaded otherwise by traditionalists. He refused, however, to celebrate the coronation in the expensive way his brother had — the 1821 coronation had cost £240,000, equal to £13,270,000 today, (of which £16,000, equal to £1,190,000 today, was merely to hire the jewels). At William's instructions, the Privy Council budgeted less than £30,000, equal to £2,240,000 today, for the coronation. When traditionalist Tories threatened to boycott what they called the "Half Crown-nation", the King retorted that they should go ahead, and that he anticipated "greater convenience of room and less heat".

After the rejection of the Second Reform Bill by the Upper House in October 1831, agitation for reform grew across the country; demonstrations grew violent in so-called "Reform Riots". In the face of popular excitement, the Grey ministry refused to accept defeat in the House of Lords, and re-introduced the Bill, which still faced difficulties in the House of Lords. Frustrated by the Lords' recalcitrance, Grey suggested that the King create a sufficient number of new peers to ensure the passage of the Reform Bill. The King objected — though he had the power to create an unlimited number of peers, he had already created 22 new peers in his Coronation Honours. William reluctantly agreed to the creation of the number of peers sufficient "to secure the success of the bill". However, the King, citing the difficulties with a permanent expansion of the Peerage, told Grey that the creations must be restricted as much as possible to the eldest sons and collateral heirs of existing peers, so that the created peerages would eventually be absorbed as subsidiary titles. This time, the Lords did not reject the bill outright, but began preparing to change its basic character through amendments. Grey and his fellow ministers decided to resign if the King did not agree to an immediate and large creation to force the bill through in its entirety. The King refused, and accepted their resignations. The King attempted to restore the Duke of Wellington to office, but Wellington had insufficient support to form a ministry and the King's popularity sank to an all-time low. Mud was slung at his carriage and he was publicly hissed. The King agreed to reappoint Grey's ministry, and to create new peers if the House of Lords continued to pose difficulties. Concerned by the threat of the creations, most of the bill's opponents abstained and the Reform Act 1832 was passed. The mob blamed William's actions on the influence of his wife and brother, and his popularity recovered.

William distrusted foreigners, particularly anyone French, which he acknowledged as a "prejudice". He also felt strongly that Britain should not interfere in the internal affairs of other nations, which brought him into conflict with the interventionist Foreign Secretary, Lord Palmerston. William was supportive of Belgian independence and, after unacceptable Dutch and French candidates were put forward, favoured Prince Leopold of Saxe-Coburg and Gotha, the widower of his niece, Charlotte, as a candidate for the newly created Belgian throne.

Though he had a reputation for tactlessness and buffoonery, William could be shrewd and diplomatic. He foresaw that the potential construction of a canal at Suez would make good relations with Egypt vital to Britain. Later in his reign he flattered the American ambassador at a dinner by announcing that he regretted not being "born a free, independent American, so much did he respect that nation, which had given birth to George Washington, the greatest man that ever lived". By exercising his personal charm, William assisted in the repair of Anglo-American relations, which had been so deeply damaged during the reign of his father.

William never visited Hanover as its King. His brother, Prince Adolphus, Duke of Cambridge, acted as viceroy there throughout William's reign as he had throughout George IV's reign. Public perception in Germany was that Britain dictated Hanoverian policy. This was not the case. In 1832, Metternich introduced laws which curbed fledging liberal movements in Germany. Britain's Foreign Secretary Lord Palmerston opposed this, and sought William's influence to cause the Hanoverian government to take the same position. The Hanoverian government instead agreed with Metternich, much to Palmerston's dismay, and William declined to intervene. The conflict between William and Palmerston over Hanover was renewed the following year when Metternich called a conference of the German states, to be held in Vienna, and Palmerston wanted Hanover to decline the invitation. Instead, the Viceroy accepted, backed fully by William. In 1833, William signed a new constitution for Hanover which empowered the middle class, gave limited power to the lower classes, and expanded the role of the parliament of Hanover. The constitution was revoked after William's death by the new king, William's brother, Prince Ernest Augustus, Duke of Cumberland.

For the remainder of his reign, William interfered actively in politics only once, in 1834; when he became the last British sovereign to choose a Prime Minister contrary to the will of Parliament. In 1834, the ministry was facing increasing unpopularity and Lord Grey retired; the Home Secretary, William Lamb, 2nd Viscount Melbourne, replaced him. Lord Melbourne retained most Cabinet members, and his ministry retained an overwhelming majority in the House of Commons. Some members of the Government, however, were anathema to the King, and increasingly left-wing policies concerned him. The previous year Grey had already pushed through a bill reforming the Protestant Church of Ireland. The Church collected tithes throughout Ireland, supported multiple bishoprics and was wealthy. However, barely an eighth of the Irish population belonged to the Church of Ireland. In some parishes, there were no Church of Ireland members at all, but there was still a priest paid for by tithes collected from the local Catholics and Presbyterians, leading to charges that idle priests were living in luxury at the expense of the Irish living at the level of subsistence. Grey's bill had reduced the number of bishoprics by half, abolished some of the sinecures and overhauled the tithe system. Further measures to appropriate the surplus revenues of the Church of Ireland were mooted by the more radical members of the Government, including Lord John Russell. The King had an especial dislike for Russell, calling him "a dangerous little Radical."

In November 1834, the Leader of the House of Commons and Chancellor of the Exchequer, John Charles Spencer, Viscount Althorp, inherited a peerage, thus removing him from the House of Commons to the Lords. Melbourne had to appoint a new Commons leader and a new Chancellor (who by long custom, must be drawn from the Commons), but the only candidate that Melbourne felt suitable to replace Althorp as Commons leader was Lord John Russell, whom William (and many others) found unacceptable due to his Radical politics. William claimed that the ministry had been weakened beyond repair and used the removal of Lord Althorp — who had previously indicated that he would retire from politics upon becoming a peer — as the pretext for the dismissal of the entire ministry. With Lord Melbourne gone, William chose to entrust power to a Tory, Sir Robert Peel. Since Peel was then in Italy, the Duke of Wellington was provisionally appointed Prime Minister. When Peel returned and assumed leadership of the ministry for himself, he saw the impossibility of governing because of the Whig majority in the House of Commons. Consequently, Parliament was dissolved to force fresh elections. Although the Tories won more seats than in the previous election, they were still in the minority. Peel remained in office for a few months, but resigned after a series of parliamentary defeats. Lord Melbourne was restored to the Prime Minister's office, remaining there for the rest of William's reign, and the King was forced to accept Russell as Commons leader.

The King had a mixed relationship with Lord Melbourne. Melbourne's government mooted more ideas to introduce greater democracy, such as the devolution of powers to the Legislative Council of Lower Canada, which greatly alarmed the King, who feared it would eventually lead to the loss of the colony. At first, the King bitterly opposed these proposals. William exclaimed to Canada Governor General designate Lord Gosford, "Mind what you are about in Canada ... mind me, my Lord, the Cabinet is not my Cabinet; they had better take care or by God, I will have them impeached." When William's son Augustus Fitzclarence enquired of his father whether the King would be entertaining during Ascot week, William gloomily replied, "I cannot give any dinners without inviting the ministers, and I would rather see the devil than any one of them in my house." Nevertheless, William approved the Cabinet's recommendations for reform. Despite his disagreements with Lord Melbourne, the King wrote warmly to congratulate the Prime Minister when he triumphed in the adultery case brought against him concerning Lady Caroline Norton — he had refused to permit Melbourne to resign when the case was first brought. The King and Prime Minister eventually found a modus vivendi; Melbourne applying tact and firmness when called for; while William realised that his First Minister was far less radical in his politics than the King had feared.

Both the King and Queen were fond of their niece, Princess Victoria of Kent. Their attempts to forge a close relationship with the girl were frustrated by the conflict between the King and the Duchess of Kent, the young princess's mother. The King, angered at what he took to be disrespect from the Duchess to his wife, took the opportunity at what proved to be his final birthday banquet in August 1836 to settle the score. Speaking to those assembled at the banquet, who included the Duchess and Princess Victoria, William expressed his hope that he would survive until Princess Victoria was 18 so that the Duchess of Kent would never be Regent. He said, "I trust to God that my life may be spared for nine months longer ... I should then have the satisfaction of leaving the exercise of the Royal authority to the personal authority of that young lady, heiress presumptive to the Crown, and not in the hands of a person now near me, who is surrounded by evil advisers and is herself incompetent to act with propriety in the situation in which she would be placed." The speech was so shocking that Victoria burst into tears, while her mother sat in silence and was only with difficulty persuaded not to leave immediately after dinner (the two left the next day). William's outburst undoubtedly contributed to Victoria's tempered view of him as "a good old man, though eccentric and singular". William survived, though mortally ill, to the month after Victoria's coming of age. "Poor old man!", Victoria wrote as he was dying, "I feel sorry for him; he was always personally kind to me."

William was "very much shaken and affected" by the death of his eldest daughter, Sophia, Lady de L'Isle, in childbirth in April 1837. William and his eldest son, George, Earl of Munster, were estranged at the time, but William hoped that a letter of condolence from Munster signalled a reconciliation. His hopes were not fulfilled and Munster, still thinking he had not been given sufficient money or patronage, remained bitter to the end.

Queen Adelaide attended the dying William devotedly, not going to bed herself for more than ten days. William IV died from heart failure in the early hours of the morning of 20 June 1837 at Windsor Castle, where he was buried. As he had no living legitimate issue, the Crown of the United Kingdom passed to Princess Victoria of Kent, the only child of Edward Augustus, Duke of Kent, George III's fourth son. Under Salic Law, a woman could not rule Hanover; thus, the Hanoverian Crown went to George III's fifth son, Ernest Augustus, Duke of Cumberland. William's death thus ended the personal union of Britain and Hanover, which had persisted since 1714. The main beneficiaries of his will were his eight surviving children by Mrs. Jordan. Although William IV is not the direct ancestor of the later monarchs of the United Kingdom, he has many notable descendants through his illegitimate family with Mrs. Jordan, including Prime Minister David Cameron, TV presenter Adam Hart-Davis, author and statesman Duff Cooper, and the Duke of Fife, who married Queen Victoria's granddaughter Louise.

William's reign was short, but eventful. The ascendancy of the House of Commons and the corresponding decline of the House of Lords were marked by the Reform Crisis, during which the threat of flooding the Upper House with peers was used effectively for the first time by a ministry. The weakening of the House of Lords continued during the nineteenth century, and culminated during the twentieth century with the passage of the Parliament Act 1911. The same threat which had been used during the Reform Crisis — the threat to flood the House of Lords by creating several new peers — was used to procure its passage.

The reduction in the influence of the Crown was clearly indicated by the events of William's reign, especially the dismissal of the Melbourne ministry. The crisis relating to Melbourne's dismissal also indicated the reduction in the King's influence with the people. During the reign of George III, the King could have dismissed one ministry, appointed another, dissolved Parliament, and expected the people to vote in favour of the new administration. Such was the result of a dissolution in 1784, after the dismissal of the Fox-North Coalition, and 1807, after the dismissal of William Wyndham Grenville, 1st Baron Grenville. But when William IV dismissed the Melbourne ministry, the Tories under Sir Robert Peel were not able to win the ensuing elections. The King's ability to influence the opinion of the people, and therefore national policy, had been reduced. None of William's successors has attempted to remove a government or appoint another against the wishes of Parliament. William understood that as a constitutional monarch he was powerless to act against the opinion of Parliament. He said, "I have my view of things, and I tell them to my ministers. If they do not adopt them, I cannot help it. I have done my duty."

During his reign great reforms were enacted by Parliament including the Factory Act, preventing child labour, the Abolition Act, emancipating slaves in the colonies, and the Poor Law, standardising provision for the destitute. He attracted criticism from reformers, who felt that reform did not go far enough, and from reactionaries, who felt that reform went too far. The modern interpretation is that he failed to satisfy either political extreme by trying to find compromise between two bitterly opposed factions, but in the process proved himself more capable as a constitutional monarch than many had supposed.