Samael

Dark angel, Samael!!!
Samael's name has the somewhat contradictory meaning of "Splendorous poisonous
one." A very mysterious and confusing angel from Hebrew mythology. Samael
appears as a huge winged snake, and while being an angel is a leader of demons
as well. Some interpret him as being a fallen angel, and later Jewish
interpretations have him as the Serpent in the Garden of Eden myth, but that
does not match up with a lot of his descriptions within earlier Hebrew
scriptures. The common belief among mythologians is that he originated as a
"good" angel and over time evolved to an "angel representing the cruel/vengeful
aspect of God" to outright "demon."

see also:
Lucifer: [link]
Michael:[link]
Gabriel: [link]
Uriel : [link]
Raphael : [link]
Metatron: [link]