|This article is about the Space Marine; for the Ork Warboss, see Grimskull.|
Strybjorn Grimskull was born a barbarian in the Grimskull tribe of Fenris. He was later accepted as a Space Marine of the Space Wolf chapter, alongside Ragnar Blackmane, after he proved his bravery and honour to a Wolf Priest.
Strybjorn and Ragnar were recruited immediately after a pitched battle between their two Fenrisian tribes, the Grimskulls and the Thunderfists, in which they engaged in single combat and seriously wounded each other. Despite this tribal enmity, they were placed together during their training and later served in the same Blood Claw pack.