NOTE: This article is about the incarnation of Surtur from the Marvel Cinematic film series. The mainstream version can be found here: Surtur (Marvel).
My time has come! When my crown is reunited with the Eternal Flame, I shall be restored to my full might! I will tower over the mountains and bury my sword deep in Asgard…
I AM ASGARD'S DOOM!
~ Surtur's last words before destroying Asgard.
Surtur is a major antagonist in the 2017 Marvel film Thor: Ragnarok.
He is an immense fire demon and the Lord of Muspelheim (a realm filled fire as befits his base), who is prophesied to bring forth the cataclysmic event known as Ragnarök - where he will destroy Asgard. Due to his nature as a god, Surtur is immortal until completing the prophecy of Ragnarok and immensely powerful.
I cannot die... not until I fulfill my destiny, and lay waste to your home.
~ Surtur showing his obsession of bringing Ragnarok, even if it means killing himself.
Surtur was a sinister, cold, emotionless, remorseless and diabolical individual who would not hesitate to kill anyone who stood in his way, be it friend or foe. He was the ultimate personification of destruction; he had used his mighty powers against his enemies and had no fear to destroy everything in his path, indicating the fact that Ragnarök must happen and that only he can ensure it happens.
He seems to be only and completely committed to his destiny to bring forth Ragnarök by destroying Asgard. In fact, he didn't even take time to notice that there were no people on Asgard and Thor had Loki revived him to destroy the now near-invincible Hela; he didn't even bother to escape from the incoming destruction and instead decides to accept his fate being incinerated, implying that he's willing to forsake his life to achieve his goal.
He also appears to have a very serious, no-nonsense mindset, being visibly annoyed when Thor refused to take him seriously during their first encounter.
In his search for answers regarding the Infinity Stones, Thor is captured in Muspelheim and brought before Surtur. The Fire Lord taunts Thor and reveals to his captive that his father, Odin, no longer rules Asgard. Furthermore, with Thor's absence, he has left the realm open for attacks. Surtur claims that he will soon destroy Asgard when he unites his crown with the Eternal Flame that Odin, after taking it from Surtur millennia ago, locked in the vaults of Asgard.
However, Thor escapes his imprisonment and is able to defeat Surtur and his demon horde in battle. In order to prevent Surtur's prophecy from coming true, Thor takes Surtur's crown with him and locks it up in the vaults of Asgard after Skurge kills Surtur's pet fire dragon. When Hela invades Asgard and reanimates its fallen soldiers (known as the Berserkers) as her army, Thor realizes that Ragnarok is the only way to stop Hela and that Asgard is not defined by its location but by its people. He then orders his brother Loki to place Surtur's crown in the Eternal Flame to revive him, which Loki does so.
This calls forth Surtur, who immediately starts annihilating Asgard by impaling his own blade into the land, killing Hela and the remaining Berserkers in the process. While Thor, Loki, Valkyrie and Hulk can safely evacuate the Asgardian citizens in one of the Grandmaster's giant spaceships, they are forced to watch Ragnarök unfold as Surtur fully thrusts his blade to destroy Asgard, killing himself in the process and leaving only asteroids in its stead.
Though Surtur accomplished Ragnarok and destroyed Asgard in death, his path of destruction was nothing but in vain as Thor have evacuated all of the Asgardians and planned to transport them to Earth as their new home. However, the arriving alien warlord Thanos and the Black Order managed to kill half of the Asgardian survivors (including Heimdall and Loki) to steal the Tesseract, leaving a helpless Thor to drift in space while Hulk is sent back to Earth to warn of Thanos' arrival.
Tremble before me, Asgard! I am your reckoning!
It's a crown!
~ Surter about his crown.
But Ragnarok has already begun! You cannot stop it! I am Asgard's doom, and so are you! All will suffer, all will burn!
You cannot stop Ragnarok. Why fight it?
~ Surter about the Ragnarok.
You have made a grave mistake, Odinson.
~ Surter to Thor Odinson.
Surtur attempts to incinerate Thor using his flame sword.
Surtur holds a captive Thor.
Hulk challenges Surtur.
Surtur is being restored to full power.
Surtur's flaming stare.
Surtur in combat mode.
Thor and Surtur clashes.
Surture's demonic stare.
Surtur about to start his rampage before comically interrupted by Hulk.