Two years after the battle of Sokovia, Thor is imprisoned by the fire demon Surtur, who reveals that Thor's father Odin is no longer on Asgard. He explains that the realm will soon be destroyed during the prophesied Ragnarök, once Surtur unites his crown with the Eternal Flame that burns in Odin's vault.
Surtur is the overarching antagonist of the 2017 Marvel Cinematic Universe film Thor: Ragnarok.
Thor: Ragnarok begins with Thor's fight against Surtur (voiced by Clancy Brown), who is prophesied to bring Ragnarok, the destruction of Thor's homeworld of Asgard. In the film's cold open, Thor defeats Surtur and removes his crown, which will bring about Ragnarok when united with the Eternal Flame on Asgard.
Despite being a comedy, Thor: Ragnarok deals with pretty serious themes throughout the entirety of the movie. A very prominent theme is brotherhood. In this movie, Thor again has to deal with his relationship with his brother Loki.
Eventually, however, Thor then returned with the newly formed Revengers and then reengaged Hela, which had then resulted with Loki unleashing Surtur, who then destroyed Asgard by finally causing Ragnarök and killed Hela as a result.
Ultimately, Hela wasn't more powerful than Surtur, but the timing was on Thor's side when he was imprisoned in Muspelheim, and as much as he tried to protect his homeworld, Asgard had to be destroyed in order to save its people and defeat Hela.
Doctor Strange, the Sorcerer Supreme, appears in Ragnarok, as the post-credits scene to his debut film promised he would.
Seeking to prevent this prophecy, Odin defeated Surtur thousands of years ago, taking the source of his power, the Eternal Flame back to Asgard and confining Surtur to Muspelheim, where he remained for over 5,000 years.
1 Scarlet Witch/Wanda Maximoff That was enough to consider her near the top but Wanda Maximoff, known as Scarlet Witch, is the officially most powerful Avenger now.
In The Dark World, there were a lot of dark colors everywhere. But in Ragnarok, there were far more bright and vibrant colors. This changed the vibe of the Thor movies from being dark and serious to lighter and funner, and fans absolutely loved it.
Ragnarok is widely considered the best Thor movie and one of the best MCU projects overall. This is largely because of its side-splitting humor, incredible supporting characters, and how it reframes Thor's character.
It warrants the need to see it on a big screen. There are big vibrant shots throughout. I think even if you're not a big Marvel fan, this is still a good movie to see because it's so different. It's more of a genre film than a Marvel film.