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Alastair is a [[Demon|Whitewhite-Eyed Demoneyed demon]] <ref>[[4.09 I Know What You Did Last Summer]]</ref> responsible for torturing human souls in [[Hell]]. He is held in high esteem by many of his demon comrades, he is referred to by [[Ruby]] as " "Practically the Grand Inquisitor downstairs. " He possesses an extensive knowledge and awareness of the universe, having occult knowledge, usage of spells cast in [[Enochian]] as well as rituals.

Alastair was initially immune to Sam's psychic abilities ,<ref>[[4.09 I Know What You Did Last Summer]]</ref>, although, ironically, he is eventually killed by them.<ref name="four16">[[4.16 On the Head of a Pin]]</ref>His durability seems to exceed that of most demons', as [[Ruby's Knifeknife]], a weapon that can kill demons, could greatly damage him but could never destroy him.<ref>[[4.09 I Know What You Did Last Summer]]</ref><ref name="four16" />

As a torturer, he is an expert interrogator In in that regard, according to [[Castiel]], he had an exceptionally strong will, allowing him to sustain himself while being tortured.<ref name="four16" /> [[Meg ]] was an apprentice of him before his death.<ref name="six10">[[6.10 Caged Heat]]</ref> He tortured both [[Dean]] and [[John Winchester]], and in both instances offered to end the torment if they would become torturers themselves. Alastair reveals that the first seal was broken when Dean accepted this offer.

He also can send an [[angel ]] back to [[Heaven ]] by expelling it from its vessel.<ref>[[4.10 Heaven and Hell]]</ref><ref name="four16" /> Alastair has shown to be resistant to an angel's power of [[exorcism]].<ref>[[4.10 Heaven and Hell]]</ref> He possess knowledge of the [[Four Horsemen of the Apocalypse ]] and has demonstrated power to overwhelm a [[reaper]].<ref>[[4.15 Death Takes a Holiday]]</ref>

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 Knifeknife]], but he is unharmed. Sam and Dean escape by jumping out the church window.

Alastair appears again to [[Ruby ]] at a [[crossroads ]] where she tries to make a deal with him: giving him [[Anna Milton ]] in exchange for allowing her and the Winchesters to go free. He then makes her a counter offer, capturing and torturing her with her knife. He later has a showdown with [[Castiel]] and [[Uriel]] in which he overpowers Castiel, but is distracted from harming him by an attack from [[Dean]]. The fight is interrupted when Anna reacquires her [[Gracegrace]] from Uriel, she and Alastair then both disappear in a flash of bright light with Alastair leaving behind only Ruby's Knifeknife.

Alastair is attempting to break one of [[The the 66 Seals]] by killing two reapers [[reaper]]s 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.

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[[angel]]s. [[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 Devildevil's Trap 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.