Asriel is a bipedal Nubian goat monster. He wears a bright sand green sweatshirt with yellow stripes on it, and black pants. He also has no footwear.
Asriel, while laid-back and humorous, is actually a bit childish, known for pulling pranks, making bad jokes, etc.
However, he can be serious at times, mainly in a Genocide Route.
In a Pacifist Route, Asriel and Sans get along fine. Asriel considers him a 'good friend who's outstanding at puns.'
In a Genocide Route, however... Asriel hates Sans for obvious reasons.
Asriel and Monster Kid get along very well, almost like brothers. They live together in a treehouse, and generally are great friends.
Asriel and Frisk have never actually met in person before the True Pacifist Route and certain Neutral Routes. Frisk makes Asriel promise to protect any human that may leave the Ruins. Asriel says that if she never made him promise, Sans would "be dead where they stand".