Crymsin Ost was a Force-sensitive Human female who became a member of the Jedi Order during the latter years of the Galactic Republic. Ost later succumbed to the dark side of the Force and became a member of the Believers, a Sith cult that operated from the Cularin system. In about 21 BBY, during the Clone Wars, she traveled to the Caarimoos system and directed a Believer operation to attempt to disperse a deadly virus on the planet Caarimon and wipe out most of the Caarite species. However, she was attacked by a group of freelance agents who defeated her and prevented the infection from being released.