Few narrative arcs are more satisfying than watching a former villain gradually become one of the story’s most important heroes. Zuko in Avatar: The Last Airbender and Vegeta in Dragon Ball Z are perhaps the defining examples. Both begin as powerful exiled princes relentlessly pursuing the heroes, only to become indispensable allies — and eventually heroes in their own right. Marvel’s best redemption story belongs in that conversation, and the first Avengers: Doomsday trailer has sent viewers rushing back to revisit it.

Loki has shot up the Disney Plus streaming charts following Monday’s release of the first full Doomsday trailer. Tom Hiddleston’s God of Mischief only appears in a brief moment of the trailer while characters like Thor (Chris Hemsworth) and Steve Rogers (Chris Evans) steal the spotlight, but anyone who’s caught up knows Loki is currently positioned as one of the most important characters in the entire MCU. That makes his streaming series, Loki, essential viewing before Doomsday, which is good news since it's also one of Marvel's very best shows. And its real achievement is completing the transformation of the MCU's nastiest Phase One villain into one of the multiverse’s greatest heroes.

Loki starts out in Thor as a jealous prince of Asgard who discovers he was secretly adopted and stolen away from his Frost Giant parents. That crisis of identity leads to him becoming a full-blown supervillain in The Avengers. As a master of illusion magic, he’s “died” on multiple occasions to then go on and hatch another scheme. Thor: The Dark World and Thor: Ragnarok both explored the brotherly bond between Loki and Thor, before Thanos unceremoniously killed Loki at the start of Avengers: Infinity War. And yet, the heroes meddling with the timeline during Avengers: Endgame allowed a different version of Loki to escape with the Tesseract shortly after the Chitauri invasion of New York City.

The divergent timeline created as a result attracts the attention of a bureaucratic organization called The Time Variance Authority, or TVA, that exists outside of time and space. Loki is quickly captured by them during the peak of his villainous era, but is quickly brought up to speed on everything his original counterpart experienced. That includes his mother’s death, his reconciliation with Thor, and his death at the hands of Thanos.

Even for a sweeping franchise where magic and cosmic forces clash on a regular basis, it’s all a bit ridiculous. But after this “time-variant” watches a highlight reel of his counterpart’s memories, he emerges from the experience a changed man. Then he’s given a choice: get “pruned” (seemingly erased from existence) or work for the TVA to combat an even greater threat that’s unraveling the branching multiverse Loki he seemingly helped to create.

Loki trades in the horns and green costume for a TVA uniform and gets to work. What unfolds is a sort of buddy-cop crime thriller where Hiddleston stars opposite Owen Wilson’s charming Agent Mobius M. Mobius. Despite the somewhat silly plot hook and the shortcut the show takes to get going, Hiddleston delivers a remarkably complex performance in Loki that overcomes whatever shortcomings the show might have at first. He’s not instantly redeemed, but Loki is definitely forced to reckon with past mistakes — and plenty of other mistakes he never had the chance to make. The strange circumstances here give Hiddleston a lot of space to explore more gravitas and pathos in equal measure, and that includes one of the most endearing romances ever seen in the MCU.

Without spoiling too much, Loki season 1 ultimately kicks off a new story arc that was originally supposed to culminate in a confrontation with Kang the Conqueror as the next Avengers-level big bad. Ant-Man and the Wasp: Quantumania followed that thread with a Kang variant trapped inside the Quantum Realm.

Season 2 explores an increasingly unstable multiverse, but mostly keeps the focus on Loki and the TVA as the Asgardian winds up unstuck in time. Kang remains an important part of the story through Victor Timely, a Kang variant and inventor from the 1860s that plays a major role in the story as Loki races to prevent a looming temporal catastrophe. The result is a surprisingly emotional conclusion to the God of Mischief’s redemptive arc — one that still feels complete even after Marvel abandoned its plans for Kang and shifted the coming conflict toward Doctor Doom (Robert Downey Jr.). Loki season 2 ends on a profound revelation about the nature of the multiverse, one that positions Loki himself as a crucial part of it. In a sense, whether that looming threat is Kang or Doom hardly matters. Both seasons of Loki remain hugely important to whatever’s about to happen next.

That makes Loki essential viewing before Avengers: Doomsday, even if Marvel’s plans have changed dramatically since the series was produced. The show lays much of the groundwork for the MCU’s multiverse, but its real achievement is far more personal. It has given the God of Mischief something he’s spent centuries chasing: a genuinely glorious purpose.