Castas was a Klatoonian Bounty hunter. He was never willing to work hard for his pay, which eventually led to his death.
Castas was hired by Aurra Sing assassinate the Jedi, Mace Windu. After a few failed attempts, Castas openly shared his feelings, and quit. Aurra Sing heard him sharing his information with another client, and she shot him for betraying them.