Alioth is a character from Marvel Comics that appears in the Disney+ series Loki. Alioth is living tempest that consumes everything that is sent to the Void at the end of time after being pruned by the Time Variance Authority. It also guards the entrance of the Citadel at the End of Time, which is the home of the creator of the organization, He Who Remains.
Alioth is living tempest, a creature born from the tears in reality, and is able to consume time and space itself. A long time ago, there was a Multiversal War caused by the many versions of Kang who fought for the supremecy of their own timelines. However, one of these Variants found Alioth and another one, known as He Who Remains, made experiments on it. He Who Remains managed to harness Alitoh's power and weaponize it to end the Multiversal War by pruning the timelines, eliminating his other Variants. He then reorganized the Multiverse into a single timeline, the Sacred Timeline, and created the Time Variance Authority to maintain it without branches. Meanwhile, Alioth was settled in the Void at the end of time, where it currently lives consuming everything that is sent there by the TVA and protecting the entrance of the Citadel at the End of Time.
In the fifth episode, after Loki was pruned by Judge Ravonna Renslayer and sent to the Void, he is found by his own Variants: Kid Loki, Alligator Loki, Classic Loki and Boastful Loki. They tell Loki that they have to walk away from the place to survive and Kid Loki warns Loki to be careful to not alarm Alioth. Kid Loki explains that they are in the Void, where the Time Variance Authority sends everything that they pruned and the creature in the sky, Alioth, makes sure nothing returns. Boastful Loki says that Alioth is a living tempest that consumes all the matter and energy that arrives, being able to devour entire branched realities that are sent there in an instast. Classic Loki then states that the Void is like a shark tank, with Alioth being the shark.
After the Lokis walked to their hideout, Loki tells them that he needs to return to the TVA to find a female Loki Variant called Sylvie and, in order to do it, he will confront Alioth. Loki reminds his Variants of what they had said about Alioth. The creature is the only thing keeping them in the Void and it is a living being that they compared to a shark, so Loki concludes that if Alioth is alive, it can be killed. Loki then asks for their help to kill Alioth, but the other Lokis just laugh because they think it is impossible to do so. However, later when the Lokis see how much Loki trusts Sylvie and her determination to destroy the TVA, they agree to help. Despite this, Classic Loki explains that getting close to Alioth is extremely dangerous, so they will only help Loki get to it and nothing more.
Meanwhile at the TVA, Sylvie prunes herself, being sent to the Void, and immediately encounters Alioth. She is forced to run away as the tempest chases her, but while she is trying to escape it, she manages to link with Alioth and sees a glimpse of something beyond the Void, also realizing that the creature can be enchanted. She is rescued by Mobius, who appears driving a car. Sylvie tells Mobius that she pruned herself with the intent to find Loki in the Void, but she is now frustrated thinking that Alioth might have already devoured him. She says that she is now focused in finding the creator of the TVA and Alioth might be the answer to do it, so she asks Mobius to turn the car back to the storm. Mobius is perplexed that Sylvie wants to confront the angry cloud from which they just escaped from.
While Loki and the other Lokis are planning how to defeat the creature, Loki suggests finding a weak part as a brain or a heart to attack it. Loki thinks that Alioth is just like any other animal, so he will be distracted eating something big and give them the chance to sneak behind it and kill it. The others become uncertain about this plan and Classic Loki says that Alligator Loki thinks that they are all going to die. They become even more skeptical as they watch Alioth from afar and witness it devouring a entire ship with its crew when they appear in the Void. As Sylvie and Mobius were in their way to return to Alioth, they end up reuniting with Loki.
Loki tells Sylvie about his plan to kill Alioth, but she thinks that it is absurd and will not work. She is surprised that the other Lokis agreed with his plan, although they state that they had their doubts if it would work. Sylvie tells them that she thinks that the creator of the TVA is beyond the Void at the end of time and is using Alioth as a guard dog to protect entrance. When Loki asks what her plan is to defeat Alioth and get to the TVA ruler, she replies that she will enchant it. Loki is skeptical about her plan, but she says that it is better than trying to stab a giant cloud to death and is confident that it will work.
Later, just before confronting Alioth, Kid Loki tells them where a branched timeline will appear, so Sylvie will wait until the creature is distracted to enchant it. Loki decides to stay in the Void to help Sylvie instead of returning to the TVA with Mobius. Mobius offers the other Lokis a chance to leave the Void, but they state that the Void is their home and refuse the offer. When Loki asks them about Alioth, they reply that they managed to survive so far and will continue to do so. After the others left, Loki and Sylvie wait for a branched timeline to appear, but Loki realizes that they won't have time to wait and signs to Sylvie that he will create a distraction for Alioth. Loki uses his magic to ignite the sword Kid Loki gave him to call Alioth's attention while Sylvie is trying to enchant it. However, this fails and the creature moves towards Sylvie's direction, making Loki run in a desperate attempt to call Alioth and save her.
Suddenly, Sylvie is saved when Alioth changes its direction to consume the perfect illusion of Asgard that is being projected by Classic Loki, who returned to help the pair. While Alioth devours Asgard's illusion, Sylvie takes Loki's hand and tells him that they are going to try to enchant the creature together. Classic Loki eventually becomes tired and his illusion starts to fade, allowing Alioth to find him. Despite this, Classic Loki has no regrets and laughs that he found his "glorious purpose" while Alioth engulfs him. Right after, Alioth moves towards Sylvie and Loki, but the pair manages to enchant him just in time. The creature's eyes and mouth glow green from the enchantment and its clouds dissipate, revealing the Citadel at the End of Time, the home of the creator of the TVA.
In the final episode of the season, when Loki and Sylvie finally find the creator of the TVA, He Who Remains, he tells them the story behind the founding of the TVA and about the Multiversal War that almost led to the destruction of the Multiverse and all its timelines. He explains that he harnessed the power of Alioth after one of his Variants found the creature. He Who Remains weaponized Alioth and used it to put an end to the war that was happening because of his own Variants, before founding the TVA to prune the branches after he reorganized the Multiverse into the Sacred Timeline.