Interesting question Moriah - What are you thinking he is then - a fallen angel like Lucifer? Is that why he gets on so well with Cas as they're really brothers??? Whatever he is - I love him :-)
There is a theory that he is a fallen Angel, because he said he had a thing with Hannah in Mesopotamia. People think that he may have realized it when Sam was pumping him with humanity.
He has to be a demon, because they've shown parts of his human life before he died and went to Hell and became a demon. His son, his mother. Those rule out any theory of him being a fallen angel, anyway.
