<Tr> <Th> Nickname (s) </Th> <Td> Cass Clarence </Td> </Tr> <Tr> <Th> Species </Th> <Td> Angel (Seraph) </Td> </Tr> <P> Castiel / ˌkæstiˈɛl / is a fictional character portrayed by Misha Collins on the CW Television Network's American television series Supernatural . An Angel of the Lord, he first appears in the fourth season, and is used to introduce the theme of Christian theology to the series . In the series, Castiel brings Dean Winchester back from Hell and frequently helps him and his brother Sam in their battles with various demons and angels along the way . During his travels with the Winchesters, Castiel develops friendships with both men . As an angel, he possesses a number of supernatural abilities, including the ability to kill demons . Initially, the character demonstrates complete devotion to God and little emotion . However, his interactions and experiences with Dean Winchester and Sam Winchester, as well as certain revelations about God and his fellow angels, have a humanizing effect on him . This, despite the stress and harm it causes his character, allows him to develop an independent will as the series progresses and helps the show address topics related to free will . </P> <P> Unlike the stereotypical portrayal of television angels, Castiel does not always help people, and is willing to kill innocents if needed . Collins originally read for the part of a demon, as series creator Eric Kripke did not want fans to find out that angels were being introduced to the series . Collins prepared for the role by reading the Book of Revelation, and based his portrayal on his younger brother . Critics and fans have responded highly favorably to the character . In response, the show's creators expanded his role in the series, upgrading him to a main cast member in the fifth and sixth seasons . After being a special guest star in the seventh and eighth seasons, Collins was upgraded once again to regular cast member status for the ninth, tenth and eleventh seasons . </P>

When does castiel first show up in supernatural