Surt
Although mentioned in chapter 1, Surt does not appear in the manga until chapter 10. Long ago Surt and Odin were allies. They fought and conquered the giant Mimir together. Mimir had great power and knowledge, so after his defeat Odin took the head to keep for himself. This caused their alliance to fracture, and by the era in which the manga story begins, Surt rules the Vanir while Odin rules the Aesir, and the two races are enemies. The head of Mimir foretells Odin that Ragnarok --the end of the World-- was near, and Odin remarks on the restlessness of the Vanir of late. When we see Surt for the first and only time, it is when Loki, after stealing the Dragon Orb, offers Surt his alliance in conquering Odin and the Aesir. Surt is wise enough to see Loki cannot be trusted and declines the offer. At that, Loki summons Fenrir, the Ice Wolf, and Bloodbane, an evil dragon. It is not shown or mentioned that Loki kills Surt, although the next time we see Loki he is attacking Valhalla alone. Surt originated in Valkyrie Profile (Playstation) and does not appear anywhere else. It is worth noting the Surt and Odin are very similar in appearance, a possible hint there is some blood relation, although this is never mentioned.