Castiel is the fallen angel fom the show Supernatural. As you may know, Castiel was the one that rescued Dean fom hell since he sold his soul to the demons in a cress-road deal to save Sam from dying.
Castiel was sent by God to Grab Dean from hell because he needed to be present on the time that the apocalypse.
He becomes good friends with Sam and Dean.
"I'm the one who gripped you tight and raised you from predition."