This lore can be found by an Inquisitor on Corellia.
The Kaggath is an ancient, but rarely employed rite of the Sith. One part duel, one part large-scale dejarik-match, the Kaggath pits Sith against Sith unto humiliation and death. The challenger sets the arena, whether a planet, a star system or the entire galaxy. The two combatants must then muster their full power bases to outwit and outmaneuver each other and defeat or win over each other’s forces. When the Dark Lord of the Sith Tulak Hord fought and won his one and only Kaggath, he declared that the name of his opponent would be stricken from history–and his command was fulfilled. The Kaggath has the power not only to destroy an individual Sith, but to obliterate his entire legacy.