The Xanatosians were a group of thirteen Jedi Knights who defected from the Jedi Order during the Clone Wars in pursuit of the dark side of the Force.
They were named after Xanatos, their "patron saint", a Jedi Padawan who fell to the dark side briefly before being killed by his master, Qui-Gon Jinn. The Xanatosians saw the late Qui-Gon as a heretic for his killing Xanatos, and sought to find their way into the Netherworld of the Force to destroy Qui-Gon's Force ghost.
During the Clone Wars, the Xanatosians managed to hide their motive for some time, however were eventually discovered following an investigation by the Jedi Temple Guard. The Xanatosians who managed to evade arrest left to join Count Dooku as Dark Acolytes. Following the war, those who remained of the Xanatosians willingly became Imperial Inquisitors.
One such Xanatosian Jedi, Troumbar Qruick, attempted to betray the Inquisitorius in an attempt to return to the light side, and was consequently killed in a duel with Darth Vader after killing a fellow Xanatosian.