A rakshasa. Once there was an altercation between Vasishta’s son Shakti and the suryavanshi king Kanmashapada. Shakti cursed the king and made him a rakshasa. At that point, Vishwamitra asked his attendant Kinkara, a rakshasa to enter the king’s body. Kinkara got the king to kill all of Vasishta’s sons as per Mahabharata Adiparva Chapter 175.