Due to their similar love for battle, it's been sarcastically implied in the manga that he's Thorkell's bastard son.
Garm is of average height and has a lanky build. He keeps his hair in a 'spiked up" style and has sparse eyebrows.
Garm has a very cocky personality. He thinks of killing as a fun game and genuinely does not understand why Thorfinn would not want to kill people anymore. In a lot of ways, Garm is quite similar to Thorkell in his love of combat. Garm is quite simple in his behavior, only wishing to fight strong opponents and enjoy the thrill of battle. He seems to be a bit of a death seeker as he remarks at the end of his first fight with Thorfinn that he really thought he'd be the one to kill him in combat.
Garm is quite blunt when expressing his opinions and desires and only seems to care about the thrills of combat. He has an utter dislike for the idea of living a peaceful life as a farmer. Throughout his second interaction with Thorfinn, Garm claims that he is his friend implying that he has a warped idea about the meaning of friendship as if it is something only relating to combat. This says a lot about how he views people with those that are worthy opponents, being his friends and has no respect for those he considers weak. In fact, he does not seem to know much about life outside of fighting.
Overall Abilities: Garm is an extremely talented fighter. He showed his talent as a child by killing multiple adults with ease. He is a very skilled and agile fighter, to the point where he rivals Thorfinn.
Spear Fighting: Garm is extremely proficient at using his custom-made spear which can be split into two, becoming short spears which he dual wields. His technique of using his spear emphasizes on range and agility. He is also able to throw his spear accurately, piercing someone's neck.
As a child, Garm was ostracized by his peers and was berated by his father. After he became an adult, Floki hires Garm to kill Thorfinn when he learns that Thorfinn could be a threat to Baldr's claim to chieftaincy. When Garm realizes Thorfinn's combat prowess, he becomes obsessed with the idea of fighting to the death with him and eventually kidnaps Einar, Gudrid, and Leif in an attempt to force Thorfinn into a duel.