Raphael

The Archangel Raphael first appeared in the 3rd episode of Season 5 (Free to be You and Me). His vessel (played by Demore Barnes) was left in a catatonic state after he returned to Heaven. However, Castiel was able to summon Raphael back into his vessel to interrogate him as to where God is, while trapping him behind a wall of holy flame (made by igniting some holy oil that Castiel obtained from Jerusalem).

Raphael was the Archangel who killed Castiel at the end of Season 4. The name Raphael means "God Heals". Raphael has promised to continue hunting down Castiel to kill him again.