Exal Kressh was a female Sith Pureblood and former apprentice to the Sith Emperor during the Great Galactic War. During her time under his tutelage, Kressh managed to uncover a grim secret of her master; the Emperor had, over the years, been inserting his "essence" into various Sith. He had almost succeeded the process with her, but she escaped from his grasp. During her retreat, Kressh began plotting and decided to turn on the Empire purely out of spite of her former master. She set course for Republic space in order to fulfill her plan.
Kressh made it to the Lenico Blue Colony, where she encountered a fellow Sith apprentice by the name of Teneb Kel, who had been ordered by the Emperor to hunt her down. They had a brief duel, destroying the colony in the process, but the Pureblood woman managed to drive fear into the more inexperienced apprentice, who fled the skirmish.
She handed over the security codes for Korriban over to the Republic, allowing them to spearhead an attack directly at the Sith homeworld almost unopposed and unexpected. Kressh accompanied them on the attack, heading down to the surface of the desert planet, who was planning to destroy the Sith Academy. It was there that she again met with Kel. Again, they fought and, in the process, Kressh revealed the Emperor's scheme to the other apprentice. While the duel was in her favor, Kel's personal slave, Maggot, attempted to shoot her whilst her guard was down, which she shrugged off and blasted Maggot with Force lightning, seriously injuring him.
Despite Kel's anger and his pressing attack after what she'd done to Maggot, Kressh once again used her superior skills to regain control of their duel and all but defeated him. As she held him in a Force grip moments from pulling him into the blade of her lightsaber, distracted from events beyond his imminent death Kressh didn't see Kel pulling his ignited blade towards her back, killing her.