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Alastair was a strong-willed demon, who was capable of withstanding the interrogations of angels, he . He was also able to withstand the torture of one of his favored apprentices, Dean Winchester. The only person known to have forced Alastair to break was Sam Winchester, who tortured Alastair with his [[demon blood]]-enhanced powers for information before killing him.<ref name="four16" />

Alastair is once again made to leave [[Hell]] and assist in starting the [[Apocalypse]], much to his dissatisfaction. Now in a new [[meatsuit]], he is attempting to break one of [[the 66 Seals]] by killing two [[reaper]]s under a solstice moon. He confronts [[Dean]] and [[Sam]] in a cemetery, revealing that he had survived his encounter with [[Anna]], though the pediatrician he had been [[possessing]] did not, and gloating that the latter's wife is still looking for her husband and unaware he is dead, which he finds hilarious. Trying again to kill them, Alastair telekinetically throws Dean into a gravestone and injures him, but finds that Sam is now immune to his powers. He flees when Sam tries to [[exorcise]] him with his powers, and later returns in yet another meatsuit. When the boys become non-corporeal to better find the demons holding the reapers hostage, they track Alastair down at a funeral home warded in [[Enochian]] script against [[angels]]. As they have made themselves subject to [[ghost]]ly weaknesses in their spiritual state, Alastair traps them with an [[iron]] chain and toys with them by shooting them with rock [[salt]] as he sends a minion to kill their unconscious bodies. While their ally [[Pamela Barnes]] is able to hold off Alastair's servant for a time and thwart this aspect of Alastair's plan, she is fatally wounded by Alastair's servant in the process and later dies. Meanwhile, Alastair begins breaking the seal and succeeds in killing one [[reaper]] with [[Death's scythe]], though the boys help [[Tessa]] escape and ultimately save the seal before fleeing. Alastair later tracks Dean down alone as Sam is fighting off Alastair's minion in an attempt to save Pamela. As he begins closing in on Dean, Alastair is struck by lightning and vanishes again as he is captured by [[Castiel]].

Alastair has held Held captive by [[Castiel]] and [[Uriel]] and imprisoned in a am [[Enochian]] [[devil's trap]] since the previous episode, but he Alastair refuses to tell them anything about the slain [[angel]]s. [[Dean]] is recruited as an interrogator because he was due to formerly being Alastair's student during his time in [[Hell]]. Amused by the idea, Alastair taunts him Dean over the course of the torture session, though he concedes that reality is "too concrete" compared to Hell for Dean to adequately torture him. Dean instead tortures Alastair with [[holy water]] injected into his veins, [[salt]] poured down his mouth, and mutilation from [[Ruby's knife]], as that he admits to an unnerved Alastair he'd dreamed of doing in Hellcoats with holy water and salt. Instead of giving Dean the information he asks for regarding the angel murders, Alastair messes plays mind games with Dean by claiming that he tortured Dean's father [[John]] in Hell and even made him the same offer he'd made Dean, but that unlike his son, John was a "hero" who steadfastly refused and ultimately escaped after 100 years (ten months on Earth) of Alastair's torture. Alastair gloats that when Dean accepted the offer in 30 years (30 3 months) and began torturing souls, he broke the first of [[the 66 Seals]] and enabled [[demons]] to begin breaking the rest of them.  Having kept an eye on the devil's trap he's caught in being compromised -- later revealed to be Uriel's doing, to let Alastair kill Dean and escape to make the angels keep thinking the demons are responsible for the angel murders Uriel committed -- Alastair escapes when a devastated Dean turns his back, then begins savagely beating Dean again. He As he is about to finish Dean off and send him back to Hell, telling him he has a lot to learn, when he becomes distracted by Castiel intervening.

Castiel embeds Ruby's knife in Alastair's shoulder and uses telekinesis to twist the blade, but Alastair simply pulls the knife out and fights Castiel. He again overpowers Castiel and while he is unable to kill the angel as he admits he wishes he could, he reveals that all he can do is send him back to [[Heaven]]. Alastair begins an angel [[exorcism]], but he is stopped by [[Sam]], who has become strong enough through his consumption of [[Ruby]]'s [[demon blood]] to overpower him with ease. Agonized by Sam's psychic torture, Alastair finally reveals that he knows none of the demons, including himself and [[Lilith]], are responsible for the angel deaths. Knowing that Sam can psychically [[exorcise]] demons, he challenges Sam to exorcise him back to Hell, where he wants to be, but is shocked when Sam instead uses his enhanced power to kill him.

Alastair's death is brought up by [[Dean]], who reveals that [[Castiel]] has told him about [[Sam]] using his powers to torture and kill Alastair with ease. Dean thinks that Sam being able to do so is another sign that he is going [[dark-side]].

Alastair is again mentioned by [[Dean]], who is in disbelief that [[Sam]]'s powers were strong enough to kill Alastair but are now not even strong enough to kill a low-level [[demon]]. The reason, unknown to Dean at the time, is that Sam has not recently fed on [[demon blood]] due to a prolonged absence from [[Ruby]].

While undergoing forced withdrawal from [[demon blood]], [[Sam]] has several hallucinations, the first of which is Alastair inexplicably returning in his last [[meatsuit]]. Finding Sam locked in [[Bobby's Panic Room]] alone with him, Alastair tortures him with a knife. Eventually Alastair disappears and Sam realizes that he had been hallucinating both Alastair and the torture.

Alastair is the only [[demon]] explicitly mentioned by [[Ruby]] when she is explaining that none of the others besides herself and [[Lilith]] had known of her undercover mission for [[Lucifer]] and Lilith.

To prove that she is capable of making [[Crowley]] give into her demands, [[Meg]] reveals that she had apprenticed under Alastair in [[Hell]] like [[Dean]] had, and Dean grudgingly concedes that this means she can make Crowley do whatever she wants. Meg doesn't reveal when she undertook this apprenticeship, but it must have been before Alastair's capture in [[4.15 Death Takes a Holiday]], as he was killed in [[4.16 On the Head of a Pin|the following episode]]. She is known to have been in Hell in the time between her [[exorcism]] in [[1.22 Devil's Trap]] and her return for revenge against the Winchesters in [[2.14 Born Under a Bad Sign]]; if his words in [[4.16 On the Head of a Pin]] were true, he would have also been working on torturing and trying to tempt [[John]]'s [[soul]] at the time. Alternately, Alastair may have taught her previously in Hell at some point [[pre-series]].

Alastair is mentioned by [[Crowley]] when listing off those who underestimated the threat the Winchesters pose and paid the price for it, along with [[Lucifer]], [[Michael]], [[Lilith]], and [[Azazel]].

[[Belphegor]] mentions Dean's time in Hell, where he was tortured by Alastair, until after for 30 years until Dean accepted Alastair's deal that he would stop the torture if Dean himself would take his place. Belphegor says tells Dean he got to watch Dean him "work" and describes described the things he did to people as not torture but "art," calling himself a fan of Dean's work. Dean simply states that it was a long time ago.