Bobrok's parentage is the subject of a long-running dispute. Most sources call him a Volhynian princeling. He could have been a junior member of the Rurikid House of Ostrog or a grandson of Gediminas of Lithuania, probably one of Karijotas's sons. It has also been speculated that he held the village of Bobrka on the Boberka River as a fief from Liubartas.