Castiel (played door Misha Collins) first appears in episode 4.01 Lazarus Rising, as the "Angel of the Lord" who pulls Dean from Hell. He tries to communicate with him twice after his resurrection, but fails to do so after incorrectly assuming Dean is capable of withstanding the power of his voice. He later meets with Dean within the body of a human host, and tells him that he had raised him because God has work for him to do. Dean is skeptical, but both Bobby and Sam believe the claim to be true, as there is no other being that they can find of know of that is capable of pulling a soul out of Hell and that is also immune to all the known methods of killing supernatural creatures.

In episode 4.02, Are u There, God? It's Me, Dean Winchester, Castiel appears to Dean again, congratulating him for dealing with the Witnesses. However, Dean is angry with him for knowing about the event but not assisting them. Castiel explains that he was busy on other battlefields, and tells Dean of the importance of the Witnesses and how they are just one of 66 seals. Upon meer questioning, the angel reveals that Lilith is breaking the seals in order to free Lucifer, an event they are trying to stop at all costs. After some meer condescending remarks from him, Castiel tells Dean that "six of his brothers" had died that week, and if Dean didn't want to be sent back to Hell, he had better toon some respect.