Kalatosh Zavros was a male Togruta Jedi Master who served the Jedi Order until he later fell to the dark side and served in Darth Revan and Darth Malak's Sith Empire.
Early in his life, Kalatosh was inducted into the Jedi Order and later reached the rank of Jedi Master, training himself as a Guardian of the Order.
During the Mandalorian Wars, Kalatosh was one of the Jedi that joined the Revanchists that went against the express command of the Order. However, during the start of the Jedi Civil War, Kalatosh succumbed to the dark side and joined the Sith Empire. By this time, he wielded a purple-bladed lightsaber. In 3956 BBY, he was present on Taris until he perished in the planet's destruction by Darth Malak. With his physical body destroyed during the bombardment, he became a Force ghost and spent the centuries leading up to the Galactic War on Taris.
In 3642 BBY, he began wreaking havoc on Taris, resulting in the Jedi Order and the resurgent Sith Empire sending people to resolve the matter. The Jedi sent Ashara Zavros, Kalatosh's descendant from a long line of Force users, and the Sith sent a Sith Inquisitor, Lord Kallig, to subjugate the dark ghost and turn Ashara to the dark side.
After Kallig performed the Force walk ritual on Kalatosh and turned Ashara to the dark side, he went on to do the same to Horak-mul. Upon binding both Kalatosh and Horak-mul, the Sith Lord attempted to destroy Darth Thanaton with his newfound power. However, the power of four ghosts proved too much. As Kallig's body began to fail, the ghosts threatened to drive their captor insane, forcing Kallig to find a way to subdue them.
After repairing their body with the aid of the Mother Machine on Belsavis, Kallig journeyed to Voss to subdue the ghosts. Kalatosh, having never heard of Voss in his lifetime, called Kallig crazy. However, with the aid of a Gormak Force-shaman named Hadrik, Kallig was able to use a mind-healing ritual to subdue the ghosts.
After Kallig successfully defeated Thanaton and gained his seat on the Dark Council, the ghosts, with the exception of Horak-mul, pleaded to be freed. Their pleas, however, were refused, and Kallig took control of them.
Kalatosh Zavros' fate can vary depending on the Sith Inquisitor's choices. He may be absorbed, be freed, or he may be redeemed along with the other ghosts to presumably become one with the Force. If the latter occurs, he describes a sensation he has never felt before, which Horak-Mul claims to be what freedom feels like.