Castiel

Castiel is an angel and one of the the main protagonists who appeared in Supernatural, he is the best friend of Dean, who was been sent and tortured by freeing him from Hell.

He is played by Misha Collins who played Jacob in the Science-Fictions movie Stonehenge Apocalypse and Dylan in the series Ringer.

In the season 4, season 5, season 7, season 8, season 9 and season 10, he mostly serves as an ally of the Winchester brothers.

Arrival on Earth
At the end of the third season of Supernatural, main character Dean Winchester is in Hell after being killed by the hellhounds of the demonic antagonist Lilith. In the season four premiere "Lazarus Rising", the angel Castiel is introduced as the one who brought Dean back from Hell and resurrected him. Because merely perceiving his actual form typically results in blindness, he takes a human host—James "Jimmy" Novak, a "devout man" who prayed for it—to communicate with Dean, and tells him that he has been brought back because God has work for him. Lilith is breaking the 66 seals in order to free Lucifer, and Dean must stop her.

Trivia
Castiel shares some similarities with Tyrael from Diablo series:
 * Both are angels whom later fallen
 * Both are willing to help humans even if they ended up against his fellow angels in doing so.