Maria of Serbia, christened Helena, was the last queen of Bosnia and despoina of Serbia. As the eldest daughter of the deceased despot of Serbia, Lazar Branković, the 12-year-old Helena was given in marriage to the Bosnian prince Stephen Tomašević in 1459. She then took the name Maria, while her husband obtained the title to Serbia through her. The country was lost to the Ottomans within a few months, and the couple fled to Bosnia. Maria's husband ascended the Bosnian throne in 1461, but two years later the kingdom too fell to the Ottomans and he was executed. The widowed queen avoided capture by fleeing to the coast. Having spent a few years in Venetian Dalmatia and possibly Hungary, Maria settled in Ottoman Greece at the court of her aunts Mara and Kantakouzene, where she spent her life in a string of conflicts and legal disputes with Kantakouzene, the Republic of Ragusa, and the Athonite monasteries.

Lazar Branković was a Serbian despot, prince of Rascia from 1456 to 1458. He was the third son of Đurađ Branković and his wife Eirene Kantakouzene. He was succeeded by his elder brother, despot Stefan III Branković.