Mrnjava (Serbian: Мрњава) was a Serbian provincial nobleman, born in Zahumlje, a frontier province in the western Serbian Kingdom. Mrnjava is the eponymous founder of the notable Mrnjavčević family; his son Vukašin Mrnjavčević became the co-ruler of the Serbian Empire (1365–1371) as king during the fall of the Serbian Empire.
Mrnjava's father was "Mrnjan" (Latin: Mergnanus; fl. c. 1280-1289), a financial chancellor (Latin: camerarius, sr. kaznac, lit. chamberlain) that served King Stephen Uroš I of Serbia and his wife, Queen Helen of Anjou at the court at Trebinje (in the royal province of Travunia). Mavro Orbini wrote that the family hailed from Hum, and that the poor Mrnjava and his two sons, who later lived in Blagaj, quickly rose to prominence under Stephen Uroš IV Dušan of Serbia who sent for them to come to his court. Possibly, the family had left Hum, which had been part of the Serbian Kingdom, after the Bosnian conquest of Hum (1326), and settled in Livno (where Vukašin was allegedly born). The family most likely supported Dušan's Bosnian campaign (1350), in which he saw to reconquer Hum.
The name of his wife is unknown. It is known that he had at least two sons:
Jovan Uglješa (1320–1371), despot of Serres 1365–1371
Vukašin Mrnjavčević (1320-1371), Lord of the Serbian Land, of the Greeks, and of the Western Provinces (co-ruler of Emperor Stephen Uroš V, 1365–1371)
Gojko Mrnjavčević (d. 1371), logothete at the Serbian Imperial court (disputed)
^ Boskovic 2009, p. 2
^ a b c d Fine 1994, pp. 362-363
^ Europäische Stammtafeln II 162
^ a b Lee 1906, p. 314
^ Zprávy o zasedání královské českē společnosti nauk (1889), p. 128
^ Soulis 1984, p. 92
^ Fine 1994, p. 322
^ Miklošič 1858, p. 180, № CLXVII.