Kosara or Cossara was a Bulgarian noblewoman, related to Tsar Samuel of Bulgaria, who was married to Prince Jovan Vladimir of Duklja.
The 11th-century Byzantine historian John Skylitzes calls her a daughter of Tsar Samuel of Bulgaria, but the annotations to Skylitzes of Michael of Duklja correct this by interpolating that her father was called Theodoretos. B. Prokić, the first editor of the manuscript (Codex Vindobonensis hist. gr. 74) that contains the annotations, mistranslated the note and emended the father's name to Theodora, thereby giving Kosara the name Theodora Kosara by which she is often known in modern scholarly literature. Modern scholarship suggests that the otherwise unattested Theodoretos may have been the son of John Chryselios, magnate of Dyrrhachium and Samuel's father-in-law.
Kosara was married ca. 1000 with Jovan Vladimir, Prince of Duklja, who had been defeated and taken prisoner of Tsar Samuel. An oral tradition recorded in the 12th-century in the Chronicle of the Priest of Duklja turns the marriage into a romantic tale of Kosara visiting Vladimir in his prison cell, eventually falling in love and asking to be married to him.
The story of Vladimir and Kosara is the subject of one of the most romantic tales of early Montenegrin literature; this is the Chronicle’s description of how Vladimir and Kosara met:
It came to pass that Samuel’s daughter, Cossara, was animated and inspired by a beatific soul. She approached her father and begged that she might go down with her maids and wash the head and feet of the chained captives. Her father granted her wish, so she descended and carried out her good work. Noticing Vladimir among the prisoners, she was struck by his handsome appearance, his humility, gentleness and modesty, and the fact that he was full of wisdom and knowledge of the LORD. She stopped to talk to him, and to her his speech seemed sweeter than honey and the honeycomb.
So Kosara fell in love with the handsome captive, and begged her father for his hand. Samuel, having conquered lands, wanted to bind his new subjects to himself in a more cordial way, not only with the sheer force. He allowed the marriage, returned Duklja to his new son-in-law, and besides gave him the whole territory of Dyrrhachium, to rule them from that point on as his vassal.