Alastair is a fictional character on The CW Television Network's drama and horror television series Supernatural, appearing in its fourth season. A particularly infamous demon and torturer in Hell, he is portrayed in succession by actors Mark Rolston, Andrew Wheeler, and Christopher Heyerdahl due to his demonic ability to possess human hosts.

The fourth season of Supernatural, an American dark fantasy television series created by Eric Kripke, premiered September 18, 2008, and concluded on May 14, 2009, on The CW.