Castiel is an angel of the Lord that was ordered to pull Dean out of Hell and help him with his mission to stop the demon Lilith from breaking the 66 Seals that would release Lucifer. He seems to be very mysterious and introspective about his assignment from God. In a recent episode he revealed to Dean that his directives are to take orders from Dean. Sam is initially in awe of Castiel for which he is instantly snubbed as being exposed by Castiel by having demon's blood and for using his abilities which are strictly forbidden (due to their demonic origins). Castiel appears to be impervious and resistant to all know forms of spells and hexes as he effortlessly passed by all the seals that Bobby and Dean scribed inside the warehouse where they all formally meet (seen in the attached picture). The human vessel he chooses to inhabit is named Jimmy Novak.

Dean bears hand prints or the "Mark of Castiel" on his shoulder as a verification and reminder that he physically pulled Dean out of Hell and has threatened to put him back if he doesn't aggressively proceed in his mission to prevent the release of Lucifer. The validity of this threat is unsubstantiated as he revealed that his mission is to follow Dean's orders. More than likely a psychological tactic to motivate Dean. Although he is an Angel, Castiel has admitted certain limitations to his abilities while on Earth. His signature power appears to be instant teleportation as he is able move effortlessly from one point to the other in the blink of an eye.

Castiel's physical appearance seems to be that of an average human male who is returning from a hard day's work in a office environment. He sports a pair of dress shoes, dress slacks, white stripped dress shirt unbuttoned and loosened necktie accentuated by a beige trenchcoat. Although he has a very dire demeanor his outward appearance radiates a natural calm and serenity which makes conversation easy and direct. Castiel see's himself has a soldier and once reminded Dean he wasn't there to perch on his shoulder when Dean was complaining about "upstairs" not giving a damm about the fact earth was in turmoil.

Unlike most angels seen in the show, Castiel shows interest in humanity and is fascinated by the aspects of humanity such has free will while other angels like Uriel or Lucifer look at humanity has inferior or with contempt. Castiel also has a respect for God that many other Angel's in the show don't seam to show possibly due to the fact that nobody has seen God in so long and they feel they have been abandoned. Castiel admitted that while he sometimes questions his orders he will always follow his Father.

Also by Angel standards and the way some of the other higher up angels like Zachariah and Anna treat him, Castiel is fairly young by angelic standards.