Geirmarr is the son of King Thrym and prince of the Frost Giants, an eager and warmongering figure far quicker to bloodshed than his measured father. When word reaches Jotunheim that the sons of Odin have stolen the Sword of Surtur and slain two sentries, it is Geirmarr who presses his father for a violent response, and he plays his own part in the pursuit that awakens the northern sentries guarding the escaping princes.
He rides at the front of the assault on Asgard. Mounted on a great bear and swinging a war hammer, he shatters Thor's chariot in the thick of the battle, only for the prince to leap up his arm and past him to reach Thrym. When Thor bows and offers the sword and himself to end the war, Geirmarr shoves through the ranks, snatches the weapon, and urges his father to kill the boy rather than grant him mercy, hungry to press their near-victory to its bloody end.