Frederick II (German: Friedrich II.; 24 January 1712 – 17 August 1786) was a King in Prussia (1740 – 1772) and a King of Prussia (1772 – 1786) from the Hohenzollern dynasty. In his role as a prince - elector of the Holy Roman Empire, he was also Elector of Brandenburg. He was in personal union the sovereign prince of the Principality of Neuchâtel. He became known as Frederick the Great (Friedrich der Große) and was nicknamed Der Alte Fritz ("Old Fritz").

Interested primarily in music and philosophy and not the arts of war during his youth, Frederick unsuccessfully attempted to flee from his authoritarian father, Frederick William I, with childhood friend, Hans Hermann von Katte, whose execution he was forced to watch after they had been captured. Upon ascending to the Prussian throne, he attacked Austria and claimed Silesia during the Silesian Wars, winning military acclaim for himself and Prussia. Near the end of his life, Frederick physically connected most of his realm by conquering Polish territories in the First Partition of Poland.

Frederick was a proponent of enlightened absolutism. For years he was a correspondent of Voltaire, with whom the king had an intimate, if turbulent, friendship. He modernized the Prussian bureaucracy and civil service and promoted religious tolerance throughout his realm. Frederick patronized the arts and philosophers, and wrote flute music. Frederick is buried at his favorite residence, Sanssouci in Potsdam. Because he died childless, Frederick was succeeded by his nephew, Frederick William II of Prussia, son of his brother, Prince Augustus William of Prussia.

Frederick was born in Berlin, the son of King Frederick William I of Prussia and Sophia Dorothea of Hanover. The so-called Soldier - King, Frederick William had developed a formidable army and encouraged centralization, but was also known for his authoritarianism and temper. Sophia, on the other hand, was well mannered and well educated. Her father, George, Elector of Hanover, was the heir of Queen Anne of Great Britain. George succeeded as King George I of Great Britain in 1714.

The birth of Frederick was welcomed by his grandfather with more than usual pleasure, as two of his grandsons had already died at an early age. Frederick William wished his sons and daughters that they be educated not as royalty, but as simple folk. He had been educated by a Frenchwoman, Madame de Montbail, who later became Madame de Rocoulle, and he wished that she educate his children. Frederick was brought up by Huguenot governesses and tutors and learned French and German simultaneously. In spite of his father's desire that his education be entirely religious and pragmatic, the young Frederick, with the help of his tutor Jacques Duhan, procured for himself a three thousand volume secret library of poetry, Greek and Roman classics, and French philosophy to supplement his official lessons.

Although Frederick William I was raised a devout Calvinist, he feared he was not of the elect. To avoid the possibility of Frederick being motivated by the same concerns the king ordered that his heir not be taught about predestination. Although he was largely irreligious, Frederick adopted this tenet of Calvinism, despite the king's efforts. Some scholars have speculated that the crown prince did this to spite his father.

In 1732, Queen Sophia Dorothea attempted to orchestrate a dual marriage of Frederick and his sister Wilhelmina with Amelia and Frederick, the children of her brother, King George II of Great Britain. Fearing an alliance between Prussia and Great Britain, Field Marshal von Seckendorff, the Austrian ambassador in Berlin, bribed Field Marshal von Grumbkow and Benjamin Reichenbach, the Prussian Minister of War and Prussian ambassador in London, respectively. The pair discreetly slandered the British and Prussian courts in the eyes of the two kings. Angered by the idea of the effete Frederick being so honored by Britain, Frederick William presented impossible demands to the British, such as Prussia acquiring Jülich and Berg, leading to the collapse of the marriage proposal.

Frederick found an ally in his sister, Wilhelmina, with whom he remained close for life. At age 16, Frederick had formed an attachment to the king's 13 year old page, Peter Karl Christoph Keith. Wilhelmina recorded that the two "soon became inseparable. Keith was intelligent, but without education. He served my brother from feelings of real devotion, and kept him informed of all the king's actions."

When he was 18, Frederick plotted to flee to England with Katte and other junior army officers. While the royal retinue was near Mannheim in the Electoral Palatinate, Robert Keith, Peter's brother, had an attack of conscience when the conspirators were preparing to escape and begged Frederick William for forgiveness on 5 August 1730; Frederick and Katte were subsequently arrested and imprisoned in Küstrin. Because they were army officers who had tried to flee Prussia for Great Britain, Frederick William leveled an accusation of treason against the pair. The king threatened the crown prince with the death penalty, then considered forcing Frederick to renounce the succession in favor of his brother, Augustus William, although either option would have been difficult to justify to the Reichstag of the Holy Roman Empire. The king forced Frederick to watch the decapitation of his confidant Katte at Küstrin on 6 November, leaving the crown prince to faint away and suffer hallucinations for the following two days.

Frederick was granted a royal pardon and released from his cell on 18 November, although he remained stripped of his military rank. Instead of returning to Berlin, however, he was forced to remain in Küstrin and began rigorous schooling in statecraft and administration for the War and Estates Departments on 20 November. Tensions eased slightly when Frederick William visited Küstrin a year later, and Frederick was allowed to visit Berlin on the occasion of his sister Wilhelmina's marriage to Margrave Frederick of Bayreuth on 20 November 1731. The crown prince returned to Berlin after finally being released from his tutelage at Küstrin on 26 February 1732.

Frederick William considered marrying Frederick to Elisabeth of Mecklenburg - Schwerin, the niece of Empress Anna of Russia, but this plan was ardently opposed by Prince Eugene of Savoy. Frederick himself proposed marrying Maria Theresa of Austria in return for renouncing the succession. Instead, Eugene persuaded Frederick William, through Seckendorff, that the crown prince marry Elisabeth Christine of Brunswick - Bevern, a Protestant relative of the Austrian Habsburgs. Although Frederick wrote to his sister that, "There can be neither love nor friendship between us," and he considered suicide, he went along with the wedding on 12 June 1733. He had little in common with his bride and resented the political marriage as an example of the Austrian interference which had plagued Prussia since 1701. Once Frederick secured the throne in 1740, he prevented Elisabeth from visiting his court in Potsdam, granting her instead Schönhausen Palace and apartments at the Berliner Stadtschloss. Frederick bestowed the title of the heir to the throne, "Prince of Prussia", on his brother Augustus William; despite this, his wife remained devoted to him.

Frederick was restored to the Prussian Army as Colonel of the Regiment von der Goltz, stationed near Nauen and Neuruppin. When Prussia provided a contingent of troops to aid Austria during the War of the Polish Succession, Frederick studied under Prince Eugene of Savoy during the campaign against France on the Rhine. Frederick William, weakened by gout brought about by the campaign, granted Frederick Schloss Rheinsberg in Rheinsberg, north of Neuruppin. In Rheinsberg, Frederick assembled a small number of musicians, actors and other artists. He spent his time reading, watching dramatic plays, making and listening to music, and regarded this time as one of the happiest of his life. Frederick formed the "Bayard Order" to discuss warfare with his friends; Heinrich August de la Motte Fouqué was made the grand master of the gatherings.

The works of Niccolò Machiavelli, such as The Prince, were considered a guideline for the behavior of a king in Frederick's age. In 1739, Frederick finished his Anti - Machiavel, an idealistic refutation of Machiavelli. It was published anonymously in 1740, but Voltaire distributed it in Amsterdam to great popularity. Frederick's years dedicated to the arts instead of politics ended upon the 1740 death of Frederick William and his inheritance of the Kingdom of Prussia.

Before his accession, Frederick was told by D'Alembert, "The philosophers and the men of letters in every land have long looked upon you, Sire, as their leader and model." Such devotion, however, had to be tempered by political realities. When Frederick ascended the throne as "King in Prussia" in 1740, Prussia consisted of scattered territories, including Cleves, Mark, and Ravensberg in the west of the Holy Roman Empire; Brandenburg, Hither Pomerania, and Farther Pomerania in the east of the Empire; and the former Duchy of Prussia, outside of the Empire bordering the Polish - Lithuanian Commonwealth. He was titled King in Prussia because this was only part of historic Prussia; he was to declare himself King of Prussia after acquiring most of the rest in 1772.

Frederick's goal was to modernize and unite his vulnerably disconnected lands; toward this end, he fought wars mainly against Austria, whose Habsburg dynasty reigned as Holy Roman Emperors almost continuously from the 15th century until 1806. Frederick established Prussia as the fifth and smallest European great power by using the resources his frugal father had cultivated.

Desiring the prosperous Austrian province of Silesia, Frederick declined to endorse the Pragmatic Sanction of 1713, a legal mechanism to ensure the inheritance of the Habsburg domains by Maria Theresa of Austria. He was also worried that Augustus III, King of Poland and Elector of Saxony, would seek to connect his own disparate lands through Silesia. The Prussian king thus invaded Silesia the same year he took power, using as justification an obscure treaty from 1537 between the Hohenzollern and the Piast dynasty of Brieg (Brzeg). The ensuing First Silesian War (1740 – 1742), part of the War of the Austrian Succession (1740 – 1748), resulted in Frederick conquering the province (with the exception of Austrian Silesia). Austria attempted to recover Silesia in the Second Silesian War (1744 – 1745), but Frederick was victorious again and forced Austria to adhere to the previous peace terms. Prussian possession of Silesia gave the kingdom control over the Oder River.

Habsburg Austria and Bourbon France, traditional enemies, allied together in the Diplomatic Revolution of 1756 following the collapse of the Anglo - Austrian Alliance. Frederick swiftly made an alliance with Great Britain at the Convention of Westminster. As neighboring countries began conspiring against him, Frederick was determined to strike first. On 29 August 1756 his well prepared army crossed the frontier and preemptively invaded Saxony, thus beginning the Seven Years' War which lasted until 1763. He faced widespread criticism for his attack on neutral Saxony and for his forcible incorporation of the Saxony forces into the Prussian army following the Siege of Pirna in October 1756.

Facing a coalition which included Austria, France, Russia, Saxony, and Sweden, and having only Great Britain and Hanover as his allies, Frederick narrowly kept Prussia in the war despite having his territories frequently invaded. Frederick was frequently at the last gasp. On 6 January 1762, he wrote to Count Karl - Wilhelm Finck von Finckenstein, "We ought now to think of preserving for my nephew, by way of negotiation, whatever fragments of my territory we can save from the avidity of my enemies", which means, that he was resolved to seek a soldier's death on the first opportunity.

The sudden death of Empress Elizabeth of Russia led to the succession of the pro - Prussian Peter III. This "Miracle of the House of Brandenburg" led to the collapse of the anti - Prussian coalition. Although Frederick did not gain any territory in the ensuing Treaty of Hubertusburg, his ability to retain Silesia during the Silesian Wars made him and Prussia popular throughout many German speaking territories.

Late in his life Frederick also involved Prussia in the low scale War of the Bavarian Succession in 1778, in which he stifled Austrian attempts to exchange the Austrian Netherlands for Bavaria. When Emperor Joseph II tried the scheme again in 1784, Frederick created the Fürstenbund, allowing himself to be seen as a defender of German liberties, in contrast to his earlier role of attacking the imperial Habsburgs.

Frederick frequently led his military forces personally and had six horses shot from under him during battle. Frederick is often admired as one of the greatest tactical geniuses of all time, especially for his usage of the oblique order of battle. Even more important were his operational successes, especially preventing the unification of numerically superior opposing armies and being at the right place at the right time to keep enemy armies out of Prussian core territory. In a letter to his mother Maria Theresa, the Austrian co-ruler Emperor Joseph II wrote,

When the King of Prussia speaks on problems connected with the art of war, which he has studied intensively and on which he has read every conceivable book, then everything is taut, solid and uncommonly instructive. There are no circumlocutions, he gives factual and historical proof of the assertions he makes, for he is well versed in history… A genius and a man who talks admirably. But everything he says betrays the knave.

An example of the place that Frederick holds in history as a ruler is seen in Napoleon Bonaparte, who saw the Prussian king as the greatest tactical genius of all time; after Napoleon's victory of the Fourth Coalition in 1807, he visited Frederick's tomb in Potsdam and remarked to his officers, "Gentlemen, if this man were still alive I would not be here". Frederick and Napoleon are perhaps the most admiringly quoted military leaders in Clausewitz' On War. More than Frederick's use of the oblique order, Clausewitz praised particularly the quick and skillful movement of his troops.

Frederick the Great's most notable and decisive military victories on the battlefield were the Battles of Hohenfriedberg, Rossbach, and Leuthen.

Frederick developed into one of the most vociferous critics of the Polish society as he began to prepare ground for dismemberment of Poland - Lithuania in 1752 at the latest, hoping to gain territorial bridge between Pomerania, Brandenburg and East Prussian provinces. Other authors also refer to a 1731 letter to Field Marshal Dubislav Gneomar von Natzmer, where Frederick had suggested that the country would be well served by annexing Polish Prussia in order to unite the territories of the Kingdom of Prussia. Similarly, the Russian and Prussian propaganda machines tried to further the resistance of the so-called dissidents against the Catholic majority of Poland.

According to Hamish M. Scott, Frederick was eager to exploit Poland economically as his wider aim of increasing Prussia's wealth. Scott views this as a continuation of his previous violations of Polish territory in 1759 and 1761 and raids within Greater Poland until 1765. After acquiring dies from which the currency of Poland was struck he issued debased Polish coins which drove money out of Poland into Hohenzollern territory – it is estimated that it gained him 25 million thalers of profit, while causing considerable monetary problems for Poland.

Frederick for many years circulated fake currency after obtaining Polish coin dies during the conquest of Saxony. His mint master Veitel - Heine Ephraim coordinated the procedure and the worthless coins were eventually called efraimki (pol. 'efraimettes'). He also opposed attempts at political reform in Poland, and his troops bombarded custom ports in Vistula, thwarting Polish efforts to create a modern fiscal system.

Empress Catherine II took the Imperial Russian throne in 1762 after the murder of her husband, Peter III. Catherine was staunchly opposed to Prussia, while Frederick disapproved of Russia, whose troops had been allowed to freely cross the Polish - Lithuanian Commonwealth during the Seven Years' War. Despite the two monarchs' dislike of each other, Frederick and Catherine signed a defensive alliance on 11 April 1764 which guaranteed Prussian control of Silesia in return for Prussian support for Russia against Austria or the Ottoman Empire. Catherine's candidate for the Polish throne, Stanisław August Poniatowski, was then elected King of Poland in September of that year.

Frederick became concerned, however, after Russia gained significant influence over Poland in the Repnin Sejm of 1767, an act which also threatened Austria and the Ottoman Turks. In the ensuing Russo - Turkish War (1768 – 1774), Frederick supported Catherine with a subsidy of 300,000 rubles with reluctance as he did not want Russia to become even stronger through the acquisitions of Ottoman territory. The Prussian king achieved a rapprochement with Emperor Joseph and the Austrian chancellor Kaunitz.

After Russia had occupied the Danubian Principalities, Frederick's representative in Saint Petersburg, his brother Henry, convinced Frederick and Maria Theresa that the balance of power would be maintained by a tripartite division of the Polish - Lithuanian Commonwealth instead of Russia taking land from the Ottomans. In the First Partition of Poland in 1772, Frederick claimed most of the Polish province of Royal Prussia. Prussia annexed 20,000 square miles (52,000 km²) and 600,000 inhabitants, the least of the partitioning powers. However, the newly created province of West Prussia connected East Prussia and Farther Pomerania and granted Prussia control of the mouth of the Vistula River. Although Maria Theresa had reluctantly agreed to the partition, Frederick commented, "she cries, but she takes".

Frederick invited German immigrants to redevelop the province also hoping they would displace the Poles. According to the conservative German historian Gerhard Ritter, Frederick II, guided by the interests of the state but not believing in the importance of race, preferred to introduce German or Frisian workers and peasants, believing them to be more fit to build up a new civilization than the “physically and morally ruined serfs of the Polish nobility”.

Frederick himself tried to further propaganda justifying the Partitions, portraying the acquired provinces as underdeveloped and improved by Prussian rule – according to Karin Friedrich these claims were accepted for a long time in German historiography and sometimes still reflected in modern works. According to Christopher Clark, 54 percent of the area's and 75 percent of the urban populace were ethnic German Protestants. Frederick however never justified his conquests on a national basis, unlike later, nationalist, 19th century German historians. Neither did he recourse to the era of the Teutonic Knights to justify Prussian claims. Dismissive of contemporary German culture, Frederic was instead pursuing an imperialist policy, acting on the security interests of his state. The newly gained territories connected Prussia with the Germany proper, and were of major economic importance to the region. According to Polish sources, Frederick II settled 300,000 colonists on territories he had conquered, and enforced Germanization.

Frederick quickly began improving the infrastructure of West Prussia, reforming its administrative and legal code, and improving the school system. 750 new schools were built from 1772 – 1775. Both Protestant and Roman Catholic teachers taught in West Prussia, and teachers and administrators were encouraged to be able to speak both German and Polish.

Frederick looked upon many of his new citizens with scorn. He had nothing but contempt for the szlachta, the numerous Polish nobility, and wrote that Poland had "the worst government in Europe with the exception of Turkey". He considered West Prussia as uncivilized as Colonial Canada and compared the Polish peasants to the Iroquois. Polish authors have also argued that already during his early days Frederick detested Poles; thus referring to them in a letter from 1735 as "dirty" and "vile apes." In a letter to Henry, Frederick wrote about the province that "it is a very good and advantageous acquisition, both from a financial and a political point of view. In order to excite less jealousy I tell everyone that on my travels I have seen just sand, pine trees, heath land and Jews. Despite that there is a lot of work to be done; there is no order, and no planning and the towns are in a lamentable condition." Many German officials also regarded the Poles with contempt. Frederick did befriend Ignacy Krasicki, whom he asked to consecrate St. Hedwig's Cathedral in 1773. He also advised his successors to learn Polish, a policy followed by the Hohenzollern dynasty until Frederick III decided not to let William II learn the language.

Frederick managed to transform Prussia from a European backwater to an economically strong and politically reformed state. His acquisition of Silesia was orchestrated so as to provide Prussia's fledgling industries with raw materials, and he protected these industries with high tariffs and minimal restrictions on internal trade. Canals were built, including between the Vistula and the Oder, swamps were drained for agricultural cultivation, and new crops, such as the potato and the turnip, were introduced. Frederick regarded his reclamation of land in the Oderbruch as a province conquered in peace. With the help of French experts, he reorganized the system of indirect taxes, which provided the state with more revenue than direct taxes. Frederick the Great commissioned Johann Ernst Gotzkowsky to promote the trade and – to take on the competition with France – put a silk factory where soon 1,500 persons found employment. Frederick the Great followed his recommendations in the field of toll levies and import restrictions. In 1763 when Gotzkowsky went broke during a financial crisis, which started in Amsterdam, Frederick took over his porcelain factory, known as KPM, but refused to buy more of his paintings.

One of Frederick's greatest achievements included the control of grain prices, whereby government storehouses would enable civilian population to survive in needy regions, where the harvest was poor.

During the reign of Frederick, the effects of the Seven Years' War and the gaining of Silesia greatly changed the economy. The circulation of depreciated money kept prices high. To revalue the Thaler, the Mint Edict of May 1763 was proposed. This stabilized the rates of depreciated coins that would not be accepted and provided for the payments of taxes in currency of prewar value. This was replaced in northern Germany by the Reichsthaler, worth one - fourth of a Conventionsthaler. Prussia used a Thaler containing one - fourteenth of a Cologne mark of silver. Many other rulers soon followed the steps of Frederick in reforming their own currencies – this resulted in a shortage of ready money thus lowering prices.

Frederick gave his state a modern bureaucracy whose mainstay until 1760 was the able War and Finance Minister Adam Ludwig von Blumenthal, succeeded in 1764 by his nephew Joachim who ran the ministry to the end of the reign and beyond. Prussia's education system was seen as one of the best in Europe. Frederick also abolished torture and corporal punishment for most cases.

Frederick began titling himself "King of Prussia" after the acquisition of Royal Prussia (West Prussia) in 1772; the phrasing "King in Prussia" had been used since the coronation of Frederick I in Königsberg in 1701.

Frederick generally supported religious toleration, including the retention of Jesuits as teachers in Silesia, Warmia, and the Netze District after their suppression by Pope Clement XIV. Just like Catherine II, Frederick recognized the educational skills the Jesuits had as an asset for the nation. He was interested in attracting a diversity of skills to his country, whether from Jesuit teachers, Huguenot citizens, or Jewish merchants and bankers, particularly from Spain. He wanted development throughout the country, specifically in areas that he judged as needing a particular kind of development. Thus, he accepted countless Protestant weavers from Bohemia, who were fleeing from the devoutly Catholic rule of Maria Theresa. Frederick granted the weavers freedom from taxes and military service. As an example of Frederick's practical minded but not fully unprejudiced tolerance, Frederick wrote in his Testament politique that:

We have too many Jews in the towns. They are needed on the Polish border because in these areas Hebrews alone perform trade. As soon as you get away from the frontier, the Jews become a disadvantage, they form cliques, they deal in contraband and get up to all manner of rascally tricks which are detrimental to Christian burghers and merchants. I have never persecuted anyone from this or any other sect; I think, however, it would be prudent to pay attention, so that their numbers do not increase.

Jews on the Polish border were therefore encouraged to perform all the trade they could and received all the protection and support from the king as any other Prussian citizen. The success in integrating the Jews into those areas of society that Frederick encouraged them in can be seen by the role played by Gerson von Bleichröder in financing Bismarck's efforts to reunite Germany.

As under Frederick much wasteland was made arable, Prussia was looking for new colonists. Frederick repeatedly emphasized that nationality and religion were of no concern to him.

Frederick had famous buildings constructed in his capital, Berlin, most of which still exist today, such as the Berlin State Opera, the Royal Library (today the State Library Berlin), St. Hedwig's Cathedral, and Prince Henry's Palace (now the site of Humboldt University). However, the king preferred spending his time in his summer residence Potsdam, where he built the palace of Sanssouci, the most important work of Northern German rococo. Sanssouci, which translates from French as "carefree" or "without worry", was a refuge for Frederick. "Frederician Rococo" developed under Georg Wenzeslaus von Knobelsdorff.

Frederick was a gifted musician who played the transverse flute. He composed 100 sonatas for the flute as well as four symphonies. The Hohenfriedberger Marsch, a military march, was supposedly written by Frederick to commemorate his victory in the Battle of Hohenfriedberg during the Second Silesian War. His court musicians included C.P.E. Bach, Johann Joachim Quantz, Carl Heinrich Graun and Franz Benda. A meeting with Johann Sebastian Bach in 1747 in Potsdam led to Bach writing The Musical Offering.

Frederick also aspired to be a Platonic philosopher king like the Roman emperor Marcus Aurelius. The king joined the Freemasons in 1738 and stood close to the French Enlightenment, admiring above all its greatest thinker, Voltaire, with whom he corresponded frequently. The personal friendship of Frederick and Voltaire came to an unpleasant end after Voltaire's visit to Berlin and Potsdam in 1750 – 1753, although they reconciled from afar in later years.

In addition to his native language, German, Frederick spoke French, English, Spanish, Portuguese, and Italian; he also understood Latin, ancient and modern Greek, and Hebrew. Preferring instead French culture, Frederick disliked the German language, literature, and culture, explaining that German authors "pile parenthesis upon parenthesis, and often you find only at the end of an entire page the verb on which depends the meaning of the whole sentence". His criticism led many German writers to attempt to impress Frederick with their writings in the German language and thus prove its worthiness. Many statesmen, including Baron vom und zum Stein, were also inspired by Frederick's statesmanship. Johann Wolfgang von Goethe gave his opinion of Frederick during a visit to Strasbourg (Strassburg) by writing:

Well we had not much to say in favour of the constitution of the Reich; we admitted that it consisted entirely of lawful misuses, but it rose therefore the higher over the present French constitution which is operating in a maze of unlawful misuses, whose government displays its energies in the wrong places and therefore has to face the challenge that a thorough change in the state of affairs is widely prophesied. In contrast when we looked towards the north, from there shone Frederick, the Pole Star, around whom Germany, Europe, even the world seemed to turn ...

Aarsleff notes that before Frederick came to the throne in 1740, the Prussian Academy of Sciences (Berlin Academy) was overshadowed by similar bodies in London and Paris. Frederick made French the official language and speculative philosophy the most important topic of study. The membership was strong in mathematics and philosophy and included Immanuel Kant, Jean D'Alembert, Pierre - Louis de Maupertuis, and Etienne de Condillac. However the Academy was in a crisis for two decades at mid century, due to scandals and internal rivalries such as the debates between Newtonianism and Leibnizian views, and the personality conflict between Voltaire and Maupertuis. At a higher level Maupertuis, the director 1746 - 59 and a monarchist, argued that the action of individuals was shaped by the character of the institution that contained them, and they worked for the glory of the state. By contrast d' Alembert took a republican rather than monarchical approach and emphasized the international Republic of Letters as the vehicle for scientific advance. By 1789, however, the academy had gained an international repute while making major contributions to German culture and thought. Frederick invited Joseph - Louis Lagrange to succeed Leonhard Euler at the Berlin Academy; both were world class mathematicians. Other intellectuals attracted to the philosopher's kingdom were Francesco Algarotti, d'Argens, and Julien Offray de La Mettrie. Immanuel Kant published religious writings in Berlin which would have been censored elsewhere in Europe.

Frederick spent much of his time at Sanssouci, his favorite residence in Potsdam. There he had built the Friendship Temple as a memorial to his favourite sister, Wilhelmine. Surrounding Wilhelmine's statue, the temple's columns have portraits of four pairs of male friends from Greek Antiquity: Euryalus and Nisos, Heracles and Philoctetes, Pirithous and Theseus, as well as Orestes and Pylades. At Sanssouci Frederick entertained his most privileged guests, especially the French philosopher Voltaire, whom he asked in 1750 to come to live with him. The correspondence between Frederick and Voltaire, which spanned almost 50 years, was marked by mutual intellectual fascination. In person, however, their friendship was often contentious, as Voltaire abhorred Frederick's militarism. Voltaire's angry attack on Maupertuis, the President of Frederick's academy, provoked Frederick to burn the pamphlet publicly and put Voltaire under house arrest. Voltaire was accused by some of anonymously publishing The Private Life of the King of Prussia, wittily claiming Frederick's homosexuality and parade of male lovers, after Voltaire had left Prussia. Frederick neither admitted nor denied the contents of the book, nor ever accused Voltaire of having written it. Some years later, Voltaire and Frederick resumed their correspondence and eventually aired their mutual recriminations, to end as friends once more. After Frederick's death, his physician, Johann Georg Ritter von Zimmermann, claimed that the king had let rumors of homosexuality appear to be true in order to keep the public from knowing that his genitalia were harmed by "a cruel surgical operation" to save his life from an unnamed venereal disease that he had contracted as a young man.

Historians disagree about the nature of Frederick's sexuality, some saying that Frederick's writings indicate that he simply had greater priorities than women. The French professor Dieudonné Thiébault declared in 1804 that Frederick had mistresses at Neuruppin. In 2011, an unpublished erotic poem by Frederick was discovered amongst his letters; it was written, according to correspondence with Voltaire, in response to an Italian friend's contention that northern Europeans were not as passionate as southern Europeans. Literary historian Christopher Clark has remarked that Frederick "may well have abstained from sexual acts with anyone of either sex after his accession to the throne, and possibly even before. But if he did not do it, he certainly talked about it; the conversation of the inner court circle around him was peppered with homoerotic banter."

In 1785, Frederick II signed a “Treaty of amity and commerce” with the United States of America, recognizing the independence of the United States. The agreement included a novel clause, whereby the two leaders of the executive branches of either country guaranteed a special and humane detention for prisoners of war. Near the end of his life Frederick grew increasingly solitary. His circle of friends at Sanssouci gradually died off without replacements, and Frederick became increasingly critical and arbitrary, to the frustration of the civil service and officer corps. The populace of Berlin always cheered the king when he returned to the city from provincial tours or military reviews, but Frederick took no pleasure from his popularity with the common folk, preferring instead the company of his pet Italian greyhounds, whom he referred to as his 'marquises de Pompadour' as a jibe at the French royal mistress. Frederick died in an armchair in his study in the palace of Sanssouci on 17 August 1786.

Frederick had wished to be buried next to his greyhounds on the vineyard terrace on the side of the corps de logis of Sanssouci. His nephew and successor Frederick William II instead ordered the body to be entombed next to his father in the Potsdam Garrison Church. Near the end of World War II, Adolf Hitler ordered the coffins of Frederick and Frederick William I, as well as those of Paul von Hindenburg and his wife, transferred first to an underground bunker near Berlin, then hidden in a salt mine close to the town of Bernrode, Germany, to protect them from destruction. The US Army discovered the four coffins on 27 April 1945, behind a 6 foot thick (1.8 m) masonry wall deep within the mine, and moved them to the basement of Marburg Castle, a collection point for recovered Nazi "treasure". As part of a secret project dubbed "Operation Bodysnatch", the US Army relocated both kings first to the Elisabeth Church of Marburg and then on to Burg Hohenzollern close to the town of Hechingen. After German reunification, the body of Frederick William was entombed in the Kaiser Friedrich Mausoleum in Sanssouci's Church of Peace.

On the 205th anniversary of his death, on 17 August 1991, Frederick's casket lay in state in the court of honor of Sanssouci, covered by a Prussian flag and escorted by a Bundeswehr guard of honor. After nightfall, Frederick's body was finally laid to rest on the terrace of the vineyard of Sanssouci, according to his last will without pomp and at night ("... Im übrigen will ich, was meine Person anbetrifft, in Sanssouci beigesetzt werden, ohne Prunk, ohne Pomp und bei Nacht..." (1757))..