The Fire Dragon is a minor antagonist in the 2017 Marvel film Thor Ragnarok. He is a giant dragon from Muspelheim that serves as the pet of the fire demon Surtur.
During his confrontation with Surtur about the impending event known as Ragnarok, Thor managed to release himself from his imprisonment by Surtur, who then summons his Fire Demons to take down Thor. Eventually, Thor used his hammer to take down the demons before defeating Surtur and taking his crown. Upon witnessing this, the angry Fire Dragon freed himself from his chains, intending to kill Thor in revenge for his master's death.
When Thor called for the Bifrost Bridge to open in order to escape, the Fire Dragon managed to catch up with him. Needless to say, Skurge is currently the new Guardian of the Bridge and he was busy flirting with several Asgardian women until they gave him Thor's message. Without hesitation, Skurge managed to open the Bridge to let Thor return to Asgard, but this accidentally decapitates the Fire Dragon as his head slides across the floor, killing him and spilling his yellow blood all over Skurge and the Asgardian women.
The fire dragon's behavior and mindset seemed to be reminiscent to a loyal domesticated pet, as he displays aggressive personality when Thor breaks free from his chains and attacks his master, prompting him to enter the fight only to be hindered by chains that are binding him. He is also very persistent, as whereas Surtur's minions seemed to lost Thor, the fire dragon did not give up the chase and even managed to catch up with Thor. Unfortunately, his blind pursuit to avenge his master led to his demise, as he accidentally decapitated due to Bifrost beam that safely bringing Thor home, where the process caused his disembodied head to end up at Asgard along with the God of Thunder.