Otto, prince of Bavaria or Othon, king of Greece (Greek: Ὄθων, Βασιλεὺς τῆς Ἑλλάδος; 1 June 1815 – 26 July 1867) was made the first modern King of Greece in 1832 under the Convention of London, whereby Greece became a new independent kingdom under the protection of the Great Powers (the United Kingdom, France and the Russian Empire).

The second son of the philhellene King Ludwig I of Bavaria, Otto ascended the newly-created throne of Greece while still a minor. His government was initially run by a three-man regency council made up of Bavarian court officials. Upon reaching his majority, Otto removed the regents when they proved unpopular with the people and he ruled as an absolute monarch. Eventually his subjects’ demands for a Constitution proved overwhelming and in the face of an armed but peaceful insurrection, Otto granted a Constitution in 1843. Throughout his reign, Otto faced political challenges concerning Greece's financial weakness and the role of the government in the affairs of the Church. The politics of Greece of this era was based on affiliations with the three Great Powers, and Otto’s ability to maintain the support of the powers was key to his remaining in power. To remain strong, Otto had to play the interests of each of the Great Powers’ Greek adherents against the others, while not aggravating the Great Powers. When Greece was blockaded by the (British) Royal Navy in 1850 and again in 1853, to stop Greece from attacking the Ottoman Empire during the Crimean War, Otto’s standing amongst Greeks suffered. As a result, there was an assassination attempt on the Queen and finally, in 1862, Otto was deposed while in the countryside. He died in exile in Bavaria in 1867.

He was born Prince Otto Friedrich Ludwig of Bavaria at Schloss Mirabell in Salzburg (when it belonged for a short time to Bavaria), as second son of King Ludwig I of Bavaria and Therese of Saxe-Hildburghausen. Through his ancestor, the Bavarian Duke John II, Otto was a descendant of the Greek imperial dynasties of Comnenus and Lascaris. When he was elected king, the Great Powers extracted a pledge from Otto’s father to restrain him from hostile actions against the Ottoman Empire, and insisted on his title being that of “King of Greece” instead of “King of the Greeks”, which would imply a claim over the millions of Greeks then still under Turkish rule. Not quite 18, the young prince arrived in Greece with 3,500 Bavarian troops and three Bavarian advisors aboard the British frigate HMS Madagascar. He immediately endeared himself to his adopted country by adopting the Greek national costume and Hellenizing his name to "Othon." For this reason, some English sources call him "Otho." ("Othon" is also the French, Spanish and Portuguese version of the German name "Otto"). Othon's reign is usually divided into 3 periods: a. The years of Regency. 1832 - 1835 b. The years of Absolute Monarchy. 1835 - 1843 c. The years of Constitutional Monarchy. 1843 - 1862

The Bavarian advisors were arrayed in a Regency Council headed by Count Josef Ludwig von Armansperg, who in Bavaria as minister of finance, had recently succeeded in restoring Bavarian credit at the cost of his popularity. Von Armansperg was the President of the Privy Council and the 1st representative (or Prime Minister) of the new Greek government. The other members of the Regency Council were Karl von Abel and Georg Ludwig von Maurer with whom von Armansperg clashed often. After the King reached his majority in 1835, von Armansperg was made Arch-Secretary but was called Arch-Chancellor by the Greek press. The UK and the Rothschild bank, who were underwriting the Greek loans, insisted on financial stringency from Armansperg. The Greeks were soon more heavily taxed than under Turkish rule; they had exchanged a hated Ottoman tyranny, which they understood, for government by a foreign bureaucracy, the "Bavarocracy" (Βαυαροκρατία), which they despised. In addition, Othon showed little respect for local customs. A staunch Roman Catholic, he refused to adopt Orthodoxy, making him a heretic in the eyes of pious Greeks. Later, however, his heirs would have to be Orthodox according to the terms of the 1843 Constitution. Popular heroes and leaders of the Greek Revolution, like the Generals Theodoros Kolokotronis and Yiannis Makriyiannis, who opposed the Bavarian-dominated regency, were charged with treason, put in jail and sentenced to death; but were pardoned later, under popular pressure, while the Greek judges, who resisted the Bavarian pressure and refused to sign the death penalties (like Anastasios Polyzoidis and Georgios Tertsetis), were saluted as heroes.

King Othon’s early reign was notable for one more reason: He moved the capital of Greece from Nafplion to Athens. His first task as king was to make a detailed archaeological and topographical survey of Athens. He assigned Gustav Eduard Schaubert and Stamatios Kleanthis to complete this task. At that time Athens had a population of roughly 4,000–5,000 people, located mainly in what today covers the district of Plaka in Athens. Athens was chosen as the Greek capital for historical and sentimental reasons, not because it was a large city. A modern city plan was laid out and public buildings erected. The finest legacy of this period are the buildings of the University of Athens (1837), the Athens Polytechnic University (1837, under the name Royal School of Arts), the National Gardens of Athens (1840), the National Library of Greece (1842), the Old Royal Palace (now the Greek Parliament Building, 1843), the Old Parliament Building (1858). Schools and hospitals were established all over the (still small) Greek dominion; but the negative feelings of the people were rather neglecting this side of his reign.

In 1836-37, Othon visited Germany and married the beautiful and talented 17 year old, Duchess Amalia (Amelie) of Oldenburg (21 December 1818 - 20 May 1875). The wedding took place not in Greece, but in Oldenburg, on 22 November 1836; the marriage did not produce an heir and the new queen made herself unpopular by interfering in the government. Besides, she remained Protestant. Not entirely faithful to his wife, Othon had a liaison with Jane Digby, a notorious woman his father had previously taken as a lover.

Meanwhile, due to his overtly undermining the king, Armansperg was dismissed from his duties by King Othon immediately on his return. However, despite high hopes by the Greeks, the Bavarian Rundhart was appointed chief minister and the granting of a Constitution was again postponed. The attempts of Othon to conciliate Greek sentiment by efforts to enlarge the frontiers of his kingdom, for example, by the suggested acquisition of Crete in 1841, failed in their objective and only succeeded in embroiling him with the Great Powers.

Throughout his reign, King Othon found himself confronted by a recurring series of issues: partisanship of the Greeks, financial uncertainty, and ecclesiastical issues. Greek parties in the Othonian era were based on two factors: the political activities of the diplomatic representatives of the Great Powers: Russia, United Kingdom and France and the affiliation of Greek political figures with these diplomats. Financial uncertainty of the Othonian monarchy was the result of 1) Greece's poverty, 2) the concentration of land in the hands of a small number of wealthy “primates” like the Mavromichalis family of Mani, and 3) the promise of 60,000,000 francs in loans from the Great Powers, which kept these nations involved in Greek internal affairs and the Crown constantly seeking to please one or the other power to ensure the flow of funds. The political machinations of the Great Powers were personified in their three legates in Athens: the French Theobald Piscatory, the Russian Gabriel Catacazy, and the English Edmund Lyons. They informed their home governments on the activities of the Greeks, while serving as advisers to their respective allied parties within Greece. Othon pursued policies, such as balancing power among all the parties and sharing offices among the parties, ostensibly to reduce the power of the parties while trying to bring a pro-Othon party into being. The parties, however, became the entree into government power and financial stability. The effect of his (and his advisors') policies was to make the Great Powers’ parties more powerful, not less. The Great Powers did not support curtailing Othon’s increasing absolutism, however, which resulted in a near permanent conflict between Othon’s absolute monarchy and the power bases of his Greek subjects.

Othon found himself confronted by a number of intractable ecclesiastical issues: 1) monasticism, 2) Autocephaly, 3) the king as head of the Church and 4) toleration of other churches. His regents, Armansperg and Rundhart, established a controversial policy of suppressing the monasteries. This was very upsetting to the Church hierarchy. Russia was self-considered as stalwart defender of Orthodoxy but Orthodox believers were found in all 3 parties. Once he rid himself of his Bavarian advisers, Othon allowed the statutory dissolution of the monasteries to lapse. By tradition dated back to the Byzantine era, the king was regarded by the Church as part of her head. On the issue of Church's Autocephaly and his role as king within the Church, Othon was overwhelmed by the arcana of Orthodox Church doctrine and popular discontent with his Roman Catholicism (while the Queen was Protestant). In 1833, the regents had unilaterally declared the Autocephaly of the Church of Greece. This fact recognized the de facto political situation, as the Patriarch of Constantinople was partially under the political control of the Ottoman Empire. Faithful people concerned that having a Catholic as the head of the Church of Greece would weaken the Orthodox Church, criticised the unilateral declaration of Autocephaly as non-canonical. They likewise resisted the foreign, mostly Protestant, missionaries who established schools throughout Greece for the same reason. Tolerance of other religions was over-supported by some in the English Party and others educated in the West as a symbol of Greece’s progress as a liberal European state. In the end, power over the Church and education was ceded to the Russian Party, while the king maintained a veto over the decision of the Synod of Bishops. This was to keep balance and avoid discrediting Greece in the eyes of Western Europe as a backward, religiously intolerant society. Actually Greek society was very tolerant to other religions. But after 400 years of religious depression by the Ottomans, Greeks were very suspicious on imposed "liberal European progress". Such forced "progress" was viewed as one more attempt against their faith and against their own understanding of freedom, as the main motto of the Greek Revolution was"for the holy faith of Christ and the freedom of the homeland"; home and faith were inseparable, given also that the Church was the main contributor to the survival of the Greek language and Greek consciousness during Turkish occupation. Catholic communities were already established in Greece since the 13th century (Athens, Cyclades, Chios, Crete) as well as Jewish communities not only since the expulsion of Jews from Spain (1492) but even since the times of Apostle Paul. Muslim families were still living in Greece during Othon's reign, since hostility was mainly against the Ottoman state and its depressive mechanisms and not against Muslim people.

Although King Othon tried to function as an absolute monarch, as Thomas Gallant writes, he “was neither ruthless enough to be feared, nor compassionate enough to be loved, nor competent enough to be respected.” By 1843, public dissatisfaction with him had reached crisis proportions and there were demands for a Constitution. Initially Othon refused to grant a Constitution, but as soon as German troops were withdrawn from the kingdom, a popular revolt was launched. On 3 September 1843, the infantry led by Colonel Dimitris Kallergis and the respected Revolutionary captain and former President of the Athens City Council General Yiannis Makriyiannis assembled in the Square in front of the Palace in Athens. Eventually joined by much of the population of the small capital, the rebellion refused to disperse until the King agreed to grant a Constitution, which would require that there be Greeks in the Council, that he convene a permanent National Assembly and that Othon personally thank the leaders of the uprising. Left with little recourse, now that his German troops were gone, King Othon gave in to the pressure and agreed to the demands of the crowd over the objections of his opinionated Queen. This square was renamed Constitution Square (Πλατεία Συντάγματος) to commemorate (until today) the events of September 1843. Now for the first time the king had Greeks in his Council and the French party, the English Party or the Russian Party (according to which of the Great Powers’ culture they most esteemed) vied for rank and power.

The King’s prestige, which was based in large part on his support by the combined Great Powers, but mostly the support of the British, suffered in the Pacifico incident of 1850, when British Foreign Secretary Palmerston sent the British fleet to blockade the port of Piraeus with warships, to exact reparation for injustice done to a British subject.

The Great Idea (Μεγάλη Ιδέα), the dream of uniting all Greek populations of the Ottoman Empire, thereby restoring the Byzantine Empire under Christian rule, led to his contemplating to enter the Crimean War at the side of Russia against Turkey and its British and French allies in 1853; the enterprise was unsuccessful, and resulted in renewed intervention by the two Great Powers and a second blockade of Piraeus port, forcing Greece to neutrality.

In 1861, a student named Aristeidis Dosios (son of politician Konstantinos Dosios) attempted to murder Queen Amalia, and was openly hailed as a hero. His attempt, however, also prompted spontaneous feelings of monarchism and sympathy towards the royal couple among the Greek population.

While on a visit to the Peloponnese in 1862, a new coup was launched and this time a Provisional Government was set up and summoned a National Convention. Ambassadors of the Great Powers urged King Othon not to resist, and the king and queen took refuge on a British warship and returned to Bavaria the same way they had come to Greece (aboard a British warship), taking with them the Greek royal regalia which he had brought from Bavaria in 1832. It has been suggested that had Othon and Amalia borne an heir, then the King would not have been overthrown, as succession was also a major unresolved question at the time. It is also true, however, that the Constitution of 1843 made provision for his succession by his two younger brothers and their descendants.

He died in the palace of the former bishops of Bamberg, Germany, and was buried in the Theatiner Church in Munich. During his retirement, he would still wear the traditional uniform nowadays worn only by the evzones (Presidential Guards). During the rebellion in Crete against the Ottoman Empire in 1866, Othon donated most of his fortune to support the revolt by supplying it with weapons. He also made provisions for his donation to be kept secret until his death, to avoid causing political problems to the new King, George I.

It is generally accepted by historians that, although Othon failed, he deeply loved Greece as his own new homeland. His failure was mainly a result of the continuous intrigues and competence between the 3 Great Powers. Before his death, Othon asked to be buried in his own Greek traditional uniform.