Stefan Uroš IV Dušan (Serbian Cyrillic: Стефан Урош IV Душан), also known as Dušan the Mighty (Serbian Cyrillic: Душан Силни; c. 1308 – 20 December 1355), was the King of Serbia from 8 September 1331 and Emperor of the Serbs, Greeks, Bulgarians and Albanians from 16 April 1346 until his death in 1355. Dušan is considered one of the greatest medieval Balkan conquerors.

Dušan conquered a large part of southeast Europe, becoming one of the most powerful monarchs of the era. Under Dušan's rule, Serbia was the most powerful state in Southeast Europe and one of the most powerful European states. At the time, Serbia was an Eastern Orthodox, multi-ethnic, and multilingual empire that stretched from the Danube in the north to the Gulf of Corinth in the south, with its capital in Skopje. He enacted the constitution of the Serbian Empire, known as Dušan Code, perhaps the most important literary work of medieval Serbia. Dušan promoted the Serbian Church from an archbishopric to a patriarchate, completed his father's mausoleum Visoki Dečani Monastery (now a UNESCO site), and founded the monastery of the Holy Archangels, among others. Under his rule, Serbia reached its territorial, political, economic, and cultural peak.

Stefan Dušan worked to forge a coalition with Venice to address the advancing threat of the Ottoman Turks into Europe. However, his efforts were interrupted by his sudden death in December 1355 at his court in Prizren. After his death, the Serbian Empire began to weaken significantly. With the death of Dušan's successor, Emperor Stefan Uroš V, the empire was definitively divided into numerous independent Serbian states, marking what is historically referred to as the Fall of the Serbian Empire. He was originally buried in his foundation near Prizren, but his remains were later relocated to the Church of Saint Mark in Belgrade, where they rest to this day.

In 1314, Serbian King Stefan Milutin quarreled with his son, Stefan Dečanski. Milutin sent Dečanski to Constantinople to have him blinded, though he was never totally blinded. Dečanski wrote to Danilo, the bishop of Hum, asking him to intervene with his father. Danilo wrote to Archbishop Nicodemus of Serbia, who spoke with Milutin and persuaded him to recall his son. In 1320 Dečanski was permitted to return to Serbia and was given the appanage of 'Budimlje' (modern Berane), while his half-brother, Stefan Konstantin, held the province of Zeta.

Milutin became ill and died on 29 October 1321, and Konstantin was crowned king. Civil war erupted immediately, as Dečanski and his cousin, Stefan Vladislav II, claimed the throne. Konstantin refused to submit to Dečanski, who then invaded Zeta, defeating and killing Konstantin. Dečanski was crowned king on 6 January 1322 by Nicodemus, and his son, Stefan Dušan, was crowned "young king". Dečanski later granted Zeta to Dušan, indicating him as the intended heir. Since April 1326 Dušan appears in written sources as the "young king" and ruler in Zeta and Zahumlje. From that fact and the "Old Serbian genealogies and annals", in recent works, some Serbian historians write that Dušan was 14 years old probably in March, or April 1326, and that he was born in 1312, not around 1308.

In the meantime, Vladislav II mobilized local support from Rudnik, the former appanage of his father, Stefan Dragutin. Vladislav proclaimed himself king, and he was supported by the Hungarians, consolidating control over his lands and preparing for battle with Dečanski. As was the case with their fathers, Serbia was divided by the two independent rulers; in 1322 and 1323 Ragusan merchants freely visited both lands.

In 1323, war broke out between Dečanski and Vladislav. Rudnik had fallen to Dečanski by the end of 1323, and Vladislav appeared to have fled north. Vladislav was defeated in battle in late 1324 and fled to Hungary, leaving the Serbian throne to Dečanski as undisputed "king of All Serbian and Maritime lands".

Dušan was the eldest son of King Stefan Dečanski and Theodora Smilets, the daughter of emperor Smilets of Bulgaria. He was born c. 1308, or in 1312, in Serbia. In 1314 Dušan's father was exiled, and the family lived in Constantinople until his recall in 1320. Dušan became acquainted with the Byzantine Empire during his stay in its capital, learning cultural customs and the Greek language. He was interested in the arts of war; in his youth he fought exceptionally in two battles, defeating Bosnian forces in 1329 during the War of Hum, and the Bulgarian emperor Michael III Shishman in the 1330 Battle of Velbužd. Dečanski appointed his nephew Ivan Stephen (through Anna Neda) to the throne of Bulgaria in August 1330.