Harker serves in the Catachan II Jungle Fighters, among the elite killers known as the Catachan Devils, and leads his own band of these fearsome warriors, nicknamed Harker's Hellraisers. The Devils are the deadliest of an already lethal breed, veterans of countless jungle wars who fight where the killing is closest and dirtiest, and Harker's squad is counted among the most feared of their number. To those who have seen him fight he is the Stonetooth Devil, a name spoken with a mixture of awe and dread.
Even by the towering standards of Catachan he is a giant, his massive frame layered with slabs of muscle and sinew. His strength is such that he carries his heavy bolter, a weapon that normally demands a two-man team and a mount, as lightly as an ordinary soldier carries a lasgun, wielding it one-handed without breaking a sweat.
That weapon, which he calls Payback, was born in disaster. During an Ork ambush as sudden as it was savage, Harker found himself the last man standing, his lasgun's energy cells burned out from ceaseless firing. He plunged his hands into the flames where a heavy weapons team had been immolated, dragged out their fallen gun, and turned it on the greenskins in a storm of vengeance. Since that day Payback has slaughtered his enemies across the length of the galaxy.
There is no aspect of warfare that Harker has not mastered, from rescue and reconnaissance to assassination and demolition. Yet for all his versatility, when the moment comes to fight or to think his way clear, he reaches for Payback every time and lets the heavy bolter do his arguing. His commanders unleash him and his Hellraisers upon the missions no one else is expected to survive, secure in the knowledge that wherever the Stonetooth Devil goes, the enemies of the Emperor are cut down in bloody droves. He is the archetype of the Catachan hero: enormous, unkillable, and happiest amid the roar of his own guns.