Tartarus appears to be an extraterrestrial from Earth 8 with a history with Darkseid. In the past, he and Darkseid made a pact, ensuring that Darkseid would never attempt conquest of Earth 8.
Tartarus made his debut in Justice League Incarnate #1 and was created by Joshua Williamson and Dennis Culver.
Major Story Arcs
Tartarus appears on Earth 8 with a legion of soldiers, interrupting an argument between Dr. Multiverse and the Retaliators. He kills the Behemoth, ripping him in half and makes short work of Dr. Multiverse before a fully-integrated Darkseid appears. After Darkseid declares that he is unwilling to honor any pacts or agreements made by "lesser Darkseids" that he has since reabsorbed, the two begin to fight.
Despite Darkseid's fully-integrated godhead, Tartarus is able to hold his own due to his use of the Eight Rings of the Ancient Spectrum, a pastiche of Marvel Comics's Infinity Gauntlet. Despite his great power, it is not enough and Darkseid snaps his neck, killing him.
Powers and Abilities
Tartarus seemed to have immense super strength and durability. Whatever power he had was greatly enhanced by his use of the Eight Rings of the Ancient Spectrum, giving him enough durability to take a fully-integrated Darkseid's omega beams.