Tuska, who styled himself the "Daemon-Killa", is the Ork Warlord who is the leader of an Ork WAAAGH! that currently battles eternally before the Brass Citadel, the heart of Khorne's domain in the Realm of Chaos in the Warp.
Tuska was once a powerful Ork Warlord famous for his many battlefield trophies. Tuska liked nothing more than pitting his strength against something larger than he was.
In 890.M41, Great Boss Tuska's flagship Kill Kroozer Gorejaw was invaded by a daemonic entity as it carved its path through the Warp. When Tuska learned that a towering, many-headed nightmare was slaughtering its way through his crew, he strapped on his Power Klaw and sprinted towards the sounds of battle, bellowing his warcry. Meeting the beast head to head on the Gorejaw's bridge, the resultant crash between Ork and daemon was titanic, but when the fighting was over Tuska had a new set of horns with which to adorn his trophy rack.
Following his enounter with the Warp-beast, the Great Boss rounded up as many Weirdboyz as he could, and utilised them to help bypass the Imperial defences around Cadia in order to invade the Eye of Terror in his search for more daemons to fight. These Ork invaders of the Immaterium soon attracted the gaze of the Blood God when they plunged headlong through the Eye of Terror in search of fresh carnage.
Their dangerously unhinged Warlord, the self-styled "Daemon-Killa," had already made his mark upon the Eye by bringing battle to several Daemon Worlds devoted to Khorne's rivals. The Ork Warlord proved unstoppable until his WAAAGH! crash-landed on a flesh planet belonging to a mighty Daemon Prince high in the standing of Khorne known as the Blood Prince.
Battling the creature and his daemonic hordes, Tuska suffered many deep wounds and his Boyz took heavy losses. Just as the Blood Prince was about to finish Tuska, his Weirdboyz managed to distract the daemon using their psychic powers, giving Tuska enough time to impale the creature between its legs with his Power Klaw before being killed himself.
The remainder of the great Warboss' vast Greenskin horde was eventually slain to an Ork by the wrathful Blood Prince and his minions, but his joy in the murderous spectacle was such that Khorne himself ensured the Greenskin crusade rose once more on the very next dawn.
History repeated itself over and over again as the Orks fought tooth and nail, never once showing signs of surrender or despair. The Blood God was so impressed by their limitless battlelust that he eventually took the Orks into his own domain in the Realm of Chaos.
In the shadow of the Brass Citadel, his elite Bloodletter generals battle against the Daemon-Killa's undying horde on a daily basis. Each cycle, great clouds of fungal spores are released by the dying Greenskins to take root and flourish in the bloodstained foothills of the Osseous Peaks. Yet more Orks are born, grow to maturity and charge into battle once more.
This suits the Daemon-Killa just fine, for he has finally found a good fight that never ends. Such endless cycles of bloodshed are also most pleasing to the Blood God. After all, the one true constant in the galaxy is that of endless war -- Khorne himself had made sure of it.
- Codex: Chaos Daemons (6th Edition), pg. 11
- Codex: Orks (4th Edition), pg. 26