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|image= [[File:3 Alastairs.jpg]]
|actor= [http://www.imdb.com/name/nm0001679/ Mark Rolston] ([[4.09 I Know What You Did Last Summer|4.09]], [[4.10 Heaven and Hell|4.10]])<br>[http://www.imdb.com/name/nm0923766/?ref_=tt_cl_t9 Andrew Wheeler] ([[4.15 Death Takes a Holiday|4.15]])<br>[http://www.imdb.com/name/nm0382216/ Christopher Heyerdahl] ([[4.15 Death Takes a Holiday|4.15]], [[4.16 On the Head of a Pin|4.16]], [[4.21 When the Levee Breaks|4.21]])
===[[4.09 I Know What You Did Last Summer]]===
Sam and Dean find [[Anna Milton]] hiding in her church. [[Ruby]] appears and tells them to run because a powerful demon is approaching. Suddenly signs of the demon's approach break out, including a statue of the virgin Mary weeping blood. Alastair arrives. Sam attempts to exorcise him with his powers, but to no effect. Dean fights with Alastair, who asks if Dean recognizes him.
Sam stabs the demon with [[Ruby's Knife]], but he is unharmed. Sam and Dean escape by jumping out the church window.
===[[4.15 Death Takes a Holiday]]===
Alastair is attempting to break one of [[The 66 Seals]] by killing two reapers under a solstice moon. He confronts Dean and Sam in a cemetery, and injures Dean, but Sam is resistant to his powers and fights back. Alastair reveals that while his [[meatsuit]] was destroyed by [[Anna]], he himself survived. He flees when Sam tries to exorcise him with his powers and later returns in yet another meatsuit. When the boys become non-corporeal, and therefore subject to ghostly weaknesses, they track Alastair down at a funeral home and he traps them with an iron chain. He kills one reaper, but the boys rescue [[Tessa]]. Later as he confronts Dean, Alastair is captured by Castiel.
===[[4.16 On the Head of a Pin]]===
Alastair is captured by Castiel and Uriel and imprisoned in a [[devil's trap]], but he refuses to tell them anything about the slain angels. Dean is recruited as an interrogator because he was formerly Alastair's student during his time in Hell. After extensive torture, Alastair breaks free Uriel having sabotaged the Devil's Trap to prevent his role in the angelic deaths being revealed. He almost kills Dean, but is stopped by Castiel, who throws Ruby's knife and embeds it in Alastair's chest. Alastair pulls the knife out and fights Castiel. He manages to trap him against a pillar, and admits that while he is unable to kill the angel, he will send him back to Heaven. Alastair begins to chant, but he is stopped by Sam, who has become strong enough to overpower him with ease. Sam forces Alastair to talk, then kills him via his abilities.