Supernatural is a series.
Castiel [ ˌkæstiˈɛl ] is a fictional character portrayed by Misha Collins on the CW Television Network 's American television series Supernatural . Supernatural (U.S. TV series) . The pilot was viewed by an estimated 5.69 million viewers , and the ratings of the first four episodes prompted The WB to pick up the series for a full season . With its eleventh season , Supernatural became the longest-running American fantasy series . The series was renewed for a twelfth season , which aired from October 13 , 2016 , to May 18 , 2017 .