Ostrit was a courtier in the court of King Foltest, and he loved the king's sister, Adda of Temeria. Angered by the incestuous relationship between the king and his sister, and the pregnancy it led to, Ostrit cursed them.
Indeed, both the mother and the girl-child died during the labour, and they were buried. Several years later, Ostrit's curse bloomed and the girl rose as a striga, haunting the streets of Old Vizima. Ostrit was killed by the monster when Geralt of Rivia used him as a bait to draw the striga out of its crypt.
In the TV series, Ostrit is portrayed by Andrzej Słabiak.
In the game, the cinematic intro sequence features that ordeal. In the last chapters of the game, we learn more about the man when Geralt finds Ostrit's journal who spells out who was responsible for the original curse.