Marko Mrnjavčević (, ;  – 17 May 1395) was the de jure Serbian king from 1371 to 1395, while he was the de facto ruler of territory in western Macedonia centered on the town of Prilep. He is known as Prince Marko (; , Kraljević Marko, ) and King Marko (; ; ) in South Slavic oral tradition, in which he has become a major character during the period of Ottoman rule over the Balkans. Marko's father, King Vukašin, was co-ruler with Serbian Tsar Stefan Uroš V, whose reign was characterised by weakening central authority and the gradual disintegration of the Serbian Empire. Vukašin's holdings included lands in north-western Macedonia and Kosovo. In 1370 or 1371, he crowned Marko "young king"; this title included the possibility that Marko would succeed the childless Uroš on the Serbian throne.

On 26 September 1371, Vukašin was killed and his forces defeated in the Battle of Maritsa. About two months later, Tsar Uroš died. This formally made Marko the king of the Serbian land; however, Serbian noblemen, who had become effectively independent from the central authority, did not even consider to recognise him as their supreme ruler. Sometime after 1371, he became an Ottoman vassal; by 1377, significant portions 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), which was completed in 1376. Later, Marko became an Ottoman vassal and died on 17 May 1395, fighting against the Wallachians in the Battle of Rovine.

Although a ruler of modest historical significance, Marko became a major character in South Slavic oral tradition. 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 Ottoman occupation.

Life Until 1371 Marko was born about 1335 as the first son of Vukašin Mrnjavčević and his wife Alena.Fostikov 2002, pp.49–50. The patronymic "Mrnjavčević" derives from Mrnjava, described by 17th-century Ragusan historian Mavro Orbin as a minor nobleman from Zachlumia (in present-day Herzegovina and southern Dalmatia). According to Orbin, Mrnjava's sons were born in Livno in western Bosnia, where he may have moved after Zachlumia was annexed from Serbia by Bosnia in 1326.Fine 1994, pp.362–3. The Mrnjavčević family may have later supported Serbian Emperor (tsar) Stefan Dušan in his preparations to invade Bosnia as did other Zachlumian nobles, and, fearing punishment, emigrated to the Serbian Empire before the war started.Fine 1994, p.323. These preparations possibly began two years ahead of the invasion, which took place in 1350. From that year comes the earliest written reference to Marko's father Vukašin, describing him as Dušan's appointed župan (district governor) of Prilep,Stojanović 1902, p.37. which was acquired by Serbia from Byzantium in 1334 with other parts of Macedonia.Fine 1994, p.288. In 1355, at about age 47, Stefan Dušan died suddenly of a stroke.Fine 1994, p.335.

Dušan was succeeded by his 19-year-old son Uroš, who apparently regarded Marko Mrnjavčević as a man of trust. The new Emperor appointed him the head of the embassy he sent to Ragusa (now Dubrovnik, Croatia) at the end of July 1361 to negotiate peace between the empire and the Ragusan Republic after hostilities earlier that year. Although peace was not reached, Marko successfully negotiated the release of Serbian merchants from Prizren who were detained by the Ragusans and was permitted to withdraw silver deposited in the city by his family. The account of that embassy in a Ragusan document contains the earliest-known, undisputed reference to Marko Mrnjavčević.Mihaljčić 1975, p.51. Ćorović 2001, "Распад Српске Царевине". An inscription written in 1356 on a wall of a church in the Macedonian region of Tikveš, mentions a Nikola and a Marko as governors in that region, but the identity of this Marko is disputed.Mihaljčić 1975, p.77.

Dušan's death was followed by the stirring of separatist activity in the Serbian Empire. The south-western territories, including Epirus, Thessaly, and lands in southern Albania, seceded by 1357.Šuica 2000, p.15. However, the core of the state (the western lands, including Zeta and Travunia with the upper Drina Valley; the central Serbian lands; and Macedonia), remained loyal to Emperor Uroš. Nevertheless, local noblemen asserted more and more independence from Uroš' authority even in the part of the state that remained Serbian. Uroš was weak and unable to counteract these separatist tendencies, becoming an inferior power in his own domain.Fine 1994, p. 345. Serbian lords also fought each other for territory and influence.

Vukašin Mrnjavčević was a skilful politician, and gradually assumed the main role in the empire.Mihaljčić 1975, p.83. In August or September 1365 Uroš crowned him king, making him his co-ruler. By 1370, Marko's potential patrimony increased as Vukašin expanded his personal holdings from Prilep further into Macedonia, Kosovo and Metohija, acquiring Prizren, Pristina, Novo Brdo, Skopje and Ohrid. In a charter he issued on 5 April 1370, Vukašin mentioned his wife (Queen Alena) and sons (Marko and Andrijaš), signing himself as "Lord of the Serb and Greek Lands, and of the Western Provinces" ().Miklošič 1858, p.180, № CLXVII. In late 1370 or early 1371, Vukašin crowned Marko "Young King", a title given to heirs presumptive of Serbian kings to secure their position as successors to the throne. Since Uroš was childless, Marko could thus become his successor, beginning a new—Vukašin—dynasty of Serbian sovereigns, and ending the two-century Nemanjić dynasty. Most Serbian lords were unhappy with the situation, which strengthened their desire for independence from the central authority.

Vukašin sought a well-connected spouse for Marko. A princess from the Croatian House of Šubić of Dalmatia was sent by her father, Grgur, to the court of their relative Tvrtko I, the ban of Bosnia. She was supposed to be raised and married by Tvrtko's mother Jelena. Jelena was the daughter of George II Šubić, whose maternal grandfather was Serbian King Dragutin Nemanjić.Fajfrić (2000), "Први Котроманићи". The ban and his mother approved of Vukašin's idea to join the Šubić princess and Marko, and the wedding was imminent.Jireček 1911, p.430.Theiner 1860, p.97, № CXC. However, in April 1370 Pope Urban V sent Tvrtko a letter forbidding him to give the Catholic lady in marriage to the "son of His Magnificence, the King of Serbia, a schismatic" (filio magnifici viri Regis Rascie scismatico). The pope also notified King Louis I of Hungary, nominal overlord of the ban,Theiner 1860, p.97, № CLXXXIX. of the impending "offence to the Christian faith", and the marriage did not occur. Marko subsequently married Jelena (daughter of Radoslav Hlapen, the lord of Veria and Edessa and the major Serbian nobleman in southern Macedonia).Mihaljčić 1975, pp. 170–1

During the spring of 1371, Marko participated in the preparations for a campaign against Nikola Altomanović, the major lord in the west of the Empire.Mihaljčić 1975, p. 137; Fine 1994, p. 377 The campaign was planned jointly by King Vukašin and Đurađ I Balšić, lord of Zeta (who was married to Olivera, the king's daughter). In July of that year Vukašin and Marko camped with their army outside Scutari, on Balšić's territory, ready to make an incursion towards Onogošt in Altomanović's land. The attack never took place, since the Ottomans threatened the land of Despot Jovan Uglješa (lord of Serres and Vukašin's younger brother, who ruled in eastern Macedonia) and the Mrnjavčević forces were quickly directed eastward. Having sought allies in vain, the two brothers and their troops entered Ottoman-controlled territory. At the Battle of Maritsa on 26 September 1371, the Turks annihilated the Serbian army;Ćorović 2001, "Маричка погибија". the bodies of Vukašin and Jovan Uglješa were never found. The battle site, near the village of Ormenio in present-day eastern Greece, has ever since been called as Sırp Sındığı ("Serbian rout") in Turkish. The Battle of Maritsa had far-reaching consequences for the region, since it opened the Balkans to the Turks.Fine 1994, pp. 379–82

After 1371

When his father died, "young king" Marko became king and co-ruler with Emperor Uroš. The Nemanjić dynasty ended soon afterwards, when Uroš died on 2 (or 4) December 1371 and Marko became the formal sovereign of Serbia.Mihaljčić 1975, p.168. Serbian lords, however, did not recognise him, and divisions within the state increased. After the two brothers' deaths and the destruction of their armies, the Mrnjavčević family was left powerless. Lords around Marko exploited the opportunity to seize significant parts of his patrimony. By 1372, Đurađ I Balšić took Prizren and Peć, and Prince Lazar Hrebeljanović took Pristina.Šuica 2000, pp.35–6. By 1377, Vuk Branković acquired Skopje, and Albanian magnate Andrea Gropa became virtually independent in Ohrid; however, he may have remained a vassal to Marko as he had been to Vukašin. Gropa's son-in-law was Marko's relative, Ostoja Rajaković of the clan of Ugarčić from Travunia. He was one of Serbian noblemen from Zachlumia and Travunia (adjacent principalities in present-day Herzegovina) who received lands in the newly conquered parts of Macedonia during Emperor Dušan's reign.Šuica 2000, p.42. The only sizable town kept by Marko was Prilep, from which his father rose. King Marko became a petty prince ruling a relatively small territory in western Macedonia, bordered in the north by the Šar mountains and Skopje; in the east by the Vardar and the Crna Reka rivers, and in the west by Ohrid. The southern limits of his territory are uncertain. Marko shared his rule with his younger brother, Andrijaš, who had his own land. Their mother, Queen Alena, became a nun after Vukašin's death, taking the monastic name Jelisaveta, but was co-ruler with Andrijaš for some time after 1371. The youngest brother, Dmitar, lived on land controlled by Andrijaš. There was another brother, Ivaniš, about whom little is known.Fostikov 2002, p.51. When Marko became an Ottoman vassal is uncertain, but it was probably not immediately after the Battle of Maritsa.Mihaljčić 1975, pp.164–5.

At some point, Marko separated from Jelena and lived with Todora, the wife of a man named Grgur, and Jelena returned to her father in Veria. Marko later sought to reconcile with Jelena but he had to send Todora to his father-in-law. Since Marko's land was bordered on the south by Hlapen's, the reconciliation may have been political. Scribe Dobre, a subject of Marko's, transcribed a liturgical book for the church in the village of Kaluđerec, and when he finished, he composed an inscription which begins as follows:Stojanović 1902, pp.58–9 Glory to God the Finisher for ever and ever, amen, amen, amen. This book was written in Porečje, in the village called Kalugerec, in the days of the pious King Marko, when he handed over Todora the wife of Grgur to Hlapen, and took back his first-wedded wife Jelena, Hlapen's daughter.

Marko's fortress was on a hill north of present-day Prilep; its partially preserved remains are known as Markovi Kuli ("Marko's towers"). Beneath the fortress is the village of Varoš, site of the medieval Prilep. The village contains the Monastery of Archangel Michael, renovated by Marko and Vukašin, whose portraits are on the walls of the monastery's church. Marko was ktetor of the Church of Saint Sunday in Prizren, which was finished in 1371, shortly before the Battle of Maritsa. In the inscription above the church's entrance, he is called "young king".Mihaljčić 1975, p.166.