Christopher Heyerdahl is a Canadian actor who portrayed Alastair in Supernatural, the Wraith Todd in Stargate Atlantis, Sam in Van Helsing, "Swede" in Hell on Wheels, and Marcus in The Twilight Saga.

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.