To answer this question, we need to understand the characters from the Mahabharata, an ancient Indian epic.
Bheeshmaka was the father of Rukmini and the king of Vidarbha. Rukmini was one of Lord Krishna's wives. Therefore, the correct answer is C) Krishna's father-in-law. Bheeshmaka played a significant role in the story of Krishna and Rukmini's marriage.