Asriel looks like both his parents, Toriel and Asgore, having white fur. His eyes have black, slightly slit-shaped pupils and yellow scleras. He wears a red and black sweater with black jeans, and wears no shoes. Since he is a child, he is short and lacks horns.
When he turns into the God of Uber Life, he wears a white robe with a heart with black wings as its symbol. He also has a pair of angel wings. His eyes have black scleras with white pupils, similar to Sans' eyes. He also looks more mature, and has curled horns. It is unknown what he looks like when he is in his final form.
When Chara was still alive, Asriel used to bully them and often berated them for being nice. But when they died, Asriel was forced to take them to a bed of golden flowers, as God of Uber Life. The humans on the surface attacked him, thinking he had killed Chara. Asriel did not fight back, and instead showed mercy while Chara tried to take control and attack. The humans, however, did not accept Asriel's mercy and they attacked him until he collapsed into dust. When Asgore noticed this, he declared war and established the "Kill or be Killed" rule amongst the Underground.