Askeladd (アシェラッド).

A cunning, mysterious Viking who commands a mercenary band of vikings, of which Thorfinn is a member.

Askeladd was contracted by Floki to assassinate Thors, Thorfinn's father. Thorfinn became obsessed with avenging his father and joined Askeladd's band with the sole intent of killing him in a fair fight, but is always outclassed by Askeladd's combat skill.

His real name is Lucius Artorius Castus.