Marko Mrnjavčević (Serbian Cyrillic: Марко Мрњавчевић, (c. 1335 – 1395) was de jure the Serbian king from 1371 to 1395, while he was the de facto ruler of a territory in western Macedonia centered on the town of Prilep. He is known as Prince Marko(Serbian Cyrillic: Краљевић Марко, Kraljević Marko, King Marko (Bulgarian and Macedonian: Kрaли Марко) in South Slavic oral tradition, in which he has become a major character during the Ottoman occupation of the Balkans. Marko's father, King Vukašin, was the co-ruler alongside Serbian Tsar Stefan Uroš V, whose reign was marked by the weakening of the central authority and the gradual disintegration of the Serbian Empire. Vukašin's personal holdings included lands in western Macedonia, Kosovo and Metohija. In 1370 or 1371, he crowned Marko "young king"; this title included the possibility that Marko succeed the childless Uroš on the Serbian throne.
On 26 September 1371, Vukašin's forces were defeated in the Battle of Maritsa and he lost his life. About two months later, Tsar Uroš died. This formally made Marko the king of the Serbian land; however, great Serbian noblemen, who had become effectively independent from the central authority, did not even consider to recognize him as their supreme ruler. At an uncertain date after 1371, he became an Ottoman vassal. By 1377, significant parts of the territory he inherited from Vukašin were seized by other noblemen. King Marko in reality came to be a regional lord who ruled over a relatively small territory in western Macedonia. He funded the construction of the Monastery of Saint Demetrius near Skopje, better known as Marko's Monastery, finished in 1376. Marko lost his life on 17 May 1395, fighting on the Ottoman side against the Wallachians in the Battle of Rovine.
Although he was a ruler of modest historical significance, Marko became a major character in South Slavic oral tradition. In Serbian epic poetry he is named Marko Kraljević, which is rendered as "Prince Marko" in English translations of the poetry; kraljević means "king's son". He is venerated as a national hero by the Serbs, Macedonians and Bulgarians, remembered in Balkan folklore as a fearless and powerful protector of the weak, who fought against injustice and confronted the Turks during the early years of Ottoman occupation.