Loki

Loki in High School DxD (prominently featured in the anime as the main antagonist of High School DxD BorN) is the Evil God from Norse mythology.

He's portrayed as an arrogant, overconfident, and destructive deity who seeks to trigger Ragnarok (the apocalyptic end of the world in Norse lore) by attempting to kill Odin and disrupt the alliance between the Norse Gods and the Three Factions (devils, angels, and fallen angels).

Appearance-wise (in the anime), he's depicted as a young, handsome man with a sinister expression, yellow eyes, flowing gray hair, and typically wearing a distinctive robe (often white with details like jewels in adaptations).

He wields powerful Norse magic, summons legendary beasts like Fenrir (the God-devouring wolf, his son), and serves as a major villain in one key arc before being defeated and sealed by the combined efforts of characters like Issei, the Occult Research Club, and allies.

He's a classic "evil god" antagonist — proud, chaotic, and battle-loving, but ultimately stopped to prevent worldwide catastrophe.