Gunnery Sergeant Harker, nicknamed "Stonetooth" Harker by his comrades in the Catachan Jungle Fighters, is one of the most renowned warriors hailing from Catachan to ever serve in the Imperial Guard. He is so exceptionally resilient that all who have served with him believe that the creature who can kill him simply has not yet come into being. Harker serves in Colonel "Iron Hand" Straken's II Regiment of the Catachan Jungle Fighters, the equally-renowned "Catachan Devils" who have a reputation for getting the job done, whatever the odds against them. Harker is the most senior Sergeant of the regiment, and leads his hand-picked team of veterans with the patience and cunning of the most dangerous of predators. In addition to being his squad's leader, Harker doubles up as the squad's heavy weapon specialist, wielding his trusted Heavy Bolter named Payback as easily as other Guardsmen wield their Lasgun.
All Catachans have a reputation for being tough bastards. Indeed, the Death World of Catachan is renowned for being one of the most hellish places in the galaxy, where humans have to learn to shoot before they can walk to survive, and every native living form can be deadly to the unwary. Imperial Guard soldiers hailing from Catachan have a well-deserved reputation for being tough, cunning, hard to kill and extreme survivalists.
"Stonetooth" Harker is renowned for being recognised as the "toughest grox-lovin' fragger that has ever lived" by his fellow Catachan soldiers. This means that to a baseline human, Harker appears to be more of a force of nature than a mere man. Rumours and stories of his exploits abound, one of the most outlandish claims being that he chews shards of glass instead of tobacco and laughs it off. While this particular rumour might be an exaggeration, he has been known to place his hands into fire and ignore it, and easily shrug off blade cuts or gunshot wounds. To Harker, pain and bleeding are concerns for weaker soldiers, for which he personally has no time.
Sergeant Harker is a giant of a man for a non-Astartes, even by Catachan standards. His gigantic frame is covered with slabs of muscle and sinew. His strength is such that he carries his Heavy Bolter Payback as easily as a normal man might carry a Lasgun, without even breaking a sweat. Harker is a long-serving veteran of the Imperial Guard, and there is not a single aspect of warfare that he has not mastered. From rescue missions to assassination, from reconnaissance to demolitions, whatever the job, Harker will get it done. His hand-picked squad members are exceptional even among their fellow Catachans, and his squad is composed of the II Catachan's bravest veterans. Their specialty is to conduct long-range penetration raids deep behind enemy lines, unleashing havoc upon the Emperor's foes and bearing the brunt of the enemy's response when battle is finally joined.
The most famous example of Harker's bravery occurred during a battle against Tyranids on the twilight world of Jorn V, where his squad was assaulted by a pack of Raveners bursting from beneath that planet's black soil. Within seconds, his ammunition loader was torn apart by monstrous claws while the rest of his squad were trying their best to stay alive. Without missing a beat, Harker leapt onto the back of the closest beast and caught it in a bear hug, crushing the bioform's spine between his monstrous biceps despite the beast's frenzied efforts to throw him off. After dispatching the first Ravener bare-handed, Harker then coolly picked up Payback and opened fire on the rest of the swarm of Tyranids at point-blank range, ripping alien bodies apart in a shower of ichor. Having eliminated the threat, and seeing that all his comrades were dead, he stalked off to find the rest of his company.
- Codex: Imperial Guard (5th Edition), pg. 62