The name is an archaic moniker for an axe-wielding serial killer who terrorized the town of Grunwald in 1915. His story has evolved into a campfire tale the townsfolk tell to scare one another. The legend goes that the Grim Halberdier will sleep for a hundred years before returning to destroy Grunwald. As Momma Grizzly is set in 2015, the boy in the forest is highly concerned about him.
In the present day, the Grim Halberdier is known colloquially as the Axe-Man.
The children have a nursery rhyme they sing about him while taunting each other during their schoolyard games:
"Axe-Man, Axe-Man, sharpen your blade. Make all the girls and boys afraid. / Sheriff got a gun, went bang-bang-bang. If they find the Axe-Man, he is sure to hang."
He exists in the present day as Pastor Chester Cotton, still with a damaged arm due to the gunshot. He claims, however, that the wound was inflicted while he was serving in Vietnam.
The Grim Halberdier orchestrates the attack on Sammie Hagen and her daughter Emma Lee the night of Veterans Day when they are found driving on Farm Road 138 after dark, suggesting he or one of his thugs has been keeping an eye on the roads outside town. He removes Emma Lee from the car, gives her to Anvilback, and instructs him to bring her back across the river to Momma Kodi. Emma Lee describes him to Kelly as "the stinky man. He was just bones." As Cotton, he feigns inaction in order to draw out anyone willful enough to summon the bear, which is how Kelly Clegg caught his attention.
He draws her in and wins her trust, but he uses the newfound information against her to damage her reputation and her relationships. He also learns that Laylah Flaherty would be his ideal target. He kidnaps the girl from town and brings her to the woods. That night, he attempts to capture the forest boy, whom Stagger needs in order to have the most control over the Leviathan.
Kelly and her husband Garrett Clegg manage to get the boy away from the Grim Halberdier, but he taunts them with Laylah. Anvilback arrives to draw out Momma Kodi, with Drag-Belly waiting in ambush. Kodi wins the ensuing battle, but she is too exhausted to pursue the Grim Halberdier, and he escapes with Laylah.
When Kelly has taken the boy home with her and Garrett is in the hospital, the Grim Halberdier gets her arrested by placing an anonymous tip that she has injured her husband and kidnapped children. When she is in prison and everyone but Ethan seems to have abandoned her, the Grim Halberdier thinks he has won. He takes Ethan and Laylah to the clearing to prepare the sacrifice and revive Stagger.
Kelly tricks the townsfolk into following her into the woods, where they witness Cotton's transformation into the Grim Halberdier. He tries to complete the ritual, but Momma Kodi intervenes. He defeats her in combat, but Kelly manages to free Ethan and then Garrett injures the Grim Halberdier once again with Angus Branchett's Revolver. The Grim Halberdier is no match when Kodi summons her husband, Firehide. The wolf severs his arm, fractures his skull, and leaves him for dead.The Grim Halberdier is last seen sacrificing himself in Laylah's place, allowing an undead version of Stagger to come to life.