Maslun is the spirit of death and vengeance for the Algonkin Native Americans in Canada 300 years ago. He takes the shape of a wolf, and is greatly feared.
A young Algonkin named Dream-Picker, who is training to be a shaman, dreams of Maslun as a young boy. The dreams are full of horror, and as he grows, he dreams of the deaths of everyone in his village.
When Dream-Picker goes on his spirit quest to find his spirit animal, he finds Maslun instead. Maslun drives away all the other spirit animals and takes Dream-Picker for himself, devouring him in his dreams. Dream-Picker eventually wakes up and makes it back to his village in a weak state. However, others in the village soon sicken, and Dream-Picker is blamed, and exiled.
Dream-Picker spends the winter away from his tribe. The tribe has a terrrible winter and many die. The shaman of the village, Dog Leg, says they have to sacrifice Wind-in-the-Leaves, Dream-Picker's love, to stop the deaths. Dream-Picker yells out into the night in his fury, wishing for the power necessary to stop the tribe. He and Wind-in-the-Leaves sleep together that night, and Dream-Picker once again dreams of Maslun hunting him down. The tribe captures them and kills Wind-in-the-Leaves.
Maslun possesses Dream-Picker, turning him into Argent the Wolf, and he slaughters all the people in his tribe.
After that, Argent is Maslun's tool of death and vengeance, killing the guilty and evil throughout the wilderness and, later, the cities. Argent is constantly hounded by the spirits of those he killed until he died. Argent becomes obsessed with Grendel, both Hunter Rose and Christine Spar, and saw them as his opposites, but in truth they are all killers. Maslun even appears to Argent in a mystical drug hallucination once, first telling Argent that his "curse" was really his own fault, and that he had asked for it with his own rage and aggression. Maslun then transforms into the face of Grendel, the spirit of aggression. It is unclear, however, whether this was only a dream, or really Maslun.
Maslun's exact powers are undefined, but he was capable of appearing in dreams to haunt people, possibly capable of giving people a deadly fever, and capable of transforming someone's body and giving them superhuman attributes and extreme longevity.
In the original Grendel volume, which is not completely canon as its stories have since been retold in other versions, Maslun was known as Moglewai, and he apparently first encountered Dream-Picker only after Wind-in-the-Leaves ran to him when he was in exile. The tribe did not catch and kill her. Instead, Moglewai took her directly into the shadow realms and turned Dream-Picker into Argent as a punishment for sheltering Wind-in-the-Leaves. Thus in this version, Argent feels the curse comes entirely from the outside, and is not his fault. Argent also says in this story that Moglewai no longer exists: when his worshipers died out, so did he.