Stephen Tomašević or Stephen II (; – 25 May 1463) was the last sovereign from the Bosnian Kotromanić dynasty, reigning as Despot of Serbia briefly in 1459 and as King of Bosnia from 1461 until 1463.

Stephen's father, King Thomas, had great ambitions for him. An attempt to expand into Croatia by marrying Stephen to a wealthy noblewoman failed, and negotiations for a marital alliance with the Sforzas of Milan were abandoned when a more prestigious opportunity presented itself: marriage to the heiress Maria of Serbia. Celebrated in April 1459, it made Stephen the ruler of the remnants of the neighbouring country. The intent was to unite the Kingdom of Bosnia and the Serbian Despotate under Stephen to combat the expanding Ottoman Empire. However, Stephen's Catholicism made him unpopular in Orthodox Serbia. After ruling it for merely two months, he surrendered it to the encroaching Ottoman forces and fled back to his father's court, which earned him the contempt of the Hungarian king Matthias Corvinus and other Christian rulers in Europe.

Stephen succeeded his father on the throne following the latter's death on 10 July 1461 and became the first Bosnian king to receive a crown from the Holy See. The kingdom's existence, however, was increasingly threatened by the Ottomans. King Stephen had the unanimous support of his noblemen in resistance to the Ottomans, but not of the common people. He maintained an active correspondence with Pope Pius II, who forgave him for the loss of Serbia and worked with him to preserve Bosnia for Christendom. The Hungarian king was placated, but all Western monarchs contacted by Stephen refused to assist him. Confident that at least Matthias would come to his aid, Stephen refused to deliver the customary tribute to the Ottoman sultan Mehmed the Conqueror, which provoked an invasion. In May 1463, Mehmed marched into Bosnia, meeting little effective resistance, and captured Stephen, who was then beheaded. The execution marks the fall of the Kingdom of Bosnia to the Ottoman Empire.

Family Born in 1438, Stephen hailed from the House of Kotromanić as one of the two known sons of the Bosnian prince Thomas by a commoner named Vojača. The other son died as an adolescent. Stephen's father was an adulterine son of King Ostoja and a younger brother of Radivoj, who contested the rule of their cousin King Tvrtko II. Thomas was politically inactive and did not take part in the struggle between his brother and cousin, enabling his family to lead a quiet life in a period when the Ottomans tried to weaken the Kingdom of Bosnia by encouraging internal divisions. This all changed when the ailing and childless King Tvrtko II decreed that Thomas should succeed him. The King died shortly after, in November 1443, and Stephen's father ascended the throne.

King Thomas, raised as a member of the Bosnian Church, converted to Roman Catholicism in c. 1445; Stephen Tomašević later stated that he had been baptized into the Roman Catholic Church as a child, and that he had been taught Latin letters. At about that time, likely in order to allow for a peaceful solution to his protracted war with the magnate Stjepan Vukčić Kosača, King Thomas requested from Pope Eugene IV an annulment of his union with Stephen's mother. Open warfare ended in 1446 with the marriage of Stephen's father to Kosača's daughter Catherine, by whom Stephen had a half-brother named Sigismund and a half-sister named Catherine.

Marriage

In the 1450s, King Thomas vigorously searched for suitable spouses for the children from his first union. Stephen's two sisters were married off in 1451, and in 1453 Stephen too entered his father's considerations. Wishing to gain control over the allodial land of Petar Talovac, who had governed Croatia proper as ban on behalf of the Hungarian king, Thomas attempted to have Stephen marry Talovac's widow, Hedwig Garai. Kosača too hastened to marry the wealthy widow, leading to an armed conflict, but neither prevailed due to an intervention by the Republic of Venice on behalf of Talovac's heirs.

The earliest source mentioning Stephen by name dates from 30 April 1455, when Pope Callixtus III put the King of Bosnia and his son under his protection. King Thomas's ambitions for Stephen grew as he strived to establish closer relations with the Western world. In 1456, he asked the Pope to procure a bride for his son, specifying that she should be a princess from a royal house. Negotiations soon commenced about Stephen's marriage to an illegitimate daughter of Francesco I Sforza, Duke of Milan, but Stephen's father had greater expectations.

When Lazar Branković, Despot of Serbia, died in 1458, an interregnum ensued. Having left three daughters and no sons, he had no clear heir, so power was shared between his blinded brother Stephen and widow Helen Palaiologina. King Thomas took advantage of their weakness to recapture Eastern Bosnian towns he had lost to Serbia in 1445. Shortly afterwards, he entered peace negotiations with Lazar's widow, Helen Palaiologina. Abandoning the prospect of his son's marriage to a daughter of the Duke of Milan, Thomas came to an agreement with Helen: Stephen was to marry the eldest of her three daughters by Lazar, the 11-year-old Helen. The match was prestigious for Stephen not only because of the bride's descent from the Byzantine imperial family, but also because it brought the government of Serbia to the groom.

The Hungarian king Matthias Corvinus agreed to Stephen's engagement with Helen – it was in his interest to create a strong buffer zone between his realm and the Ottoman Empire by uniting the Kingdom of Bosnia and the Despotate of Serbia, which he considered Hungary's vassal states, under Stephen Tomašević. The Diet of Hungary confirmed Stephen Tomašević's right to Serbia in January 1459.

Despotism

Stephen, accompanied by his uncle Radivoj, duly set out for Serbia but narrowly escaped imprisonment during an Ottoman raid on the Bosnian royal residence of Bobovac. He arrived in Smederevo, capital of the Eastern Orthodox despotate, during the Holy Week, and ascended the Serbian throne on 21 March 1459. Michael Szilágyi, regent for the underage King Matthias, arrived at the head of an army to ensure that command over the town's fortress would be assumed by Stephen without any difficulties.

Stephen's marriage to Helen took place on 1 April 1459, the first Sunday following Easter. Following the presumably Catholic ceremony, the bride was known as Maria. He assumed the title of despot, despite the fact that the title was neither hereditary nor tied to a specific territory, but a grant from the Byzantine emperor. It is possible that his mother-in-law, a member of Byzantium's last imperial family, believed that she had the right to grant the title in the absence of an emperor. Within a week of the wedding, Stephen exiled his wife's uncle from Serbia. King Thomas boasted to the Duke of Milan that his son had been made despot "with the agreement and will of all the Rascians", but Stephen's regime was not particularly popular; chroniclers writing about his treatment of his wife's uncle cursed him as a schismatic.

It was clear from the outset that Stephen's reign in Serbia would be short-lived. The Ottoman sultan Mehmed the Conqueror considered Stephen's enthronement an unwarranted violation of his own rights, for the Ottomans too considered Serbia their vassal state. Mehmed promptly launched an attack on Smederevo in June, and there was no serious consideration of trying to defend it. King Thomas rushed to his son's aid, trying to divert the Turks by laying siege to their fortress of Hodidjed, in the middle of Bosnia. Aware that Smederevo could not withstand Mehmed's attack, Stephen surrendered the fortress on 20 June 1459. The Ottoman proceeded to annex the rest of the Serbian state to their empire within a year.

Following the fall of the town which Pope Pius II lamentably termed "the gateway to Rascia", Stephen fled to Bosnia with his family and in-laws, seeking refuge at the court of his father. The King of Hungary accused Stephen and his family of selling Smederevo Fortress to the Ottomans "for a great weight of gold", and the Pope at first believed him. Pius's own investigation appears to have come to the conclusion that Stephen did not sell the fortress, as the Pope did not repeat the claim. Ottoman, Bosnian and Serbian sources say nothing about the supposed betrayal, so the allegation is unlikely to be based on fact. The Serbian-born janissary Konstantin Mihailović and the Byzantine Greek scholar Laonikos Chalkokondyles maintained Stephen's innocence and pointed out to the strength of the Ottoman army. Both state that the Serbs within Smederevo were so unhappy with Bosnian rule and convinced that the Ottomans would prevail (and grant them more religious tolerance than the Hungarians) that they went out to meet Mehmed and presented him with keys to the city.

Kingship Accession and coronation

King Thomas died on 10 July 1461. According to later accounts, Thomas's death was plotted by Stephen and Radivoj, and even Matthias and Mehmed were implicated. Historians dismiss these allegations, however, pointing out that the King had been ill since June. Stephen ascended the throne without difficulty. He ensured that his uncle would not contest the succession by generously endowing him with land. The new monarch assumed the pompous title inherited from Tvrtko I, the first Bosnian king, styling himself as, "by the Grace of God, King of Serbia, Bosnia, the Maritime Lands, Zachlumia, Dalmatia, Croatia, and the Western lands" – regardless of the fact that Serbia had by then become an Ottoman pashaluk, that Croatia had been lost to Hungary in the 1390s, and that he had to beg the government of the Republic of Venice to allow him to take refuge in Dalmatia in case of an Ottoman attack.

Immediately upon his accession, Stephen set out to resolve all disagreements within the royal family in order to strengthen his own position. His relations with his stepmother, the 37-year-old Queen Catherine, had been strained during his father's lifetime, but he now guaranteed that she would retain her title and privileges. Her father, Stjepan Vukčić Kosača, wrote to Venetian officials that the King had "taken her as his mother", Vojača having already died by the time he ascended the throne. Kosača was the kingdom's most powerful nobleman, and had been engaged in a never-ending conflict with Stephen's father. Stephen Tomašević took the Venetians' advice to make peace with his stepgrandfather, thus finally ensuring the nobility's absolute support of their king. He then focused on improving Bosnia's economy, which became stronger than ever during his reign, and ensuring that the state would collect more profit from the flourishing metalworking trade.

Problems rose soon already in the summer of 1461, when Pavao Špirančić, who governed Croatia as ban on behalf of the Hungarian king and frequently clashed with King Thomas, seized a border town. By late summer, Stephen and Kosača were preparing to strike him jointly and divide his territory between themselves. Venice objected, fearing that the fortresses Klis and Ostrovica, paramount to the defense of Dalmatia, might fall to the Ottomans if first taken over by the Bosnians.