Darth Mantis was a strong Sith Marauder. He used the force to improve his mind which gave him control over his overwhelming power. He trained alone for many years, and was a pupil under Revan. His rank has always been a mystery. He was as powerful as a Sith Lord, and once called himself by that title, however as he gained control, he gained humility, unusual for a sith.
He would later become a teacher to Tardan He would have Tardan train in secret for many years, and Dealt with the Enemy Exar Kun, attempting to assassinate him while his apprentice trained. The Attempts failed, and later came back to Revan and Tardan, to train full time