Zab and his brother Ab are two minor gate Opener-Demons who were sent to earth and possessed the bodies of two murderers who died in a car crash that Spawn had caused outside the town of Malice, Pennsylvania. They went to a nearby diner and waited until they had 13 innocents to sacrifice. They executed them and took them to a nearby hill where they painted a mystical emblem on the ground and burned the bodies, completing an opening spell that released Urizen from his banishment and allowed him to return through the smoke. As they worked they referenced that Urizen had been forgotten over time.
Soon after Angela found and captured the demons forcing them to reveal their plans and kept them tied up until Urizen could be stopped. When he was eventually sealed up again by Spawn he forced them to tell him who sent them, the two revealed their employer to be none other than The Malebolgia. Soon after Spawn and Angela would confront and kill the Malebolgia.
It wouldn't be long before the two demons resurfaced as soon after Spawn had ordered them to help him defeat the cult of vampires known only as The Kingdom. As The Kingdom set out on its murderous rampage Spawn had tried to stop them and used Ab and Zab to force the decapitated head of the vampire Wolfram to reveal The Kingdoms plans. Knowing their plans Spawn ordered Ab and Zab to build a portal to Hell that would suck in the vampires. However after the vampires were forced into Hell an old enemy returned through the portal..... the Violator!