The Firebird is a major character from Disney's 38th full-length animated feature film, Fantasia 2000. He serves as the titular main antagonist in the film's final segment, The Firebird Suite, and is therefore the final antagonist in the film itself. His scene obviously represents death and destruction.
The Firebird appears to be a giant eagle with huge wings and is made entirely out of lava. Though his body bears some resemblance with the Spring Sprite, he lacks any pair of legs unlike her, as he morphed into lava mass whenever he traveled on the land. It is currently unclear whether he can fly like the Spring Sprite or not.
Unlike Chernabog in the original Fantasia film whom sides with the force of evil, The Firebird is a powerful, dangerous, aggressive, and treacherous fire spirit who has no alliances; he serves no one, he cannot distinguish friend from foe - he is a primal living force of destruction. He lives only to destroy and despises all that brings life and creation (ex. The Spring Sprite).
However, his only weakness is that he only destroys - he cannot create nor can he persist, as he returned to his slumber when there is nothing left for him to destroy. This explained his disappearance after destroyed much of the forest.
The Firebird Suite
The Firebird is first seen inside a mountain (more likely a volcano since nothing grows near the mountain), where the segment's protagonist, the Spring Sprite, inadvertently wakes him up. This makes him so mad that he chases after her. As he does, he burns the trees everywhere in the forest she had worked so hard on growing until, he consumes her. However, she is revived by the Elk. It is unknown what happened to the Firebird after that, although it is suggested that he comes every time a volcano erupts. Volcanoes can cause serious damage to an ecosystem, but the ecosystems are known to heal in time.
Real-Life Incident Comparison
A similar real life example of the similar incident that started by Firebird is the Mount St. Helen's 1980 eruption. Mount St. Helens's is located near a lush national park and when it erupted, much of the forest was destroyed. Many doubted the land would ever heal, but much to everyone's surprise, the area is healing, just as everything is healed in the segment.
The Firebird shares similarities with Hexxus from the 1992 animated film by 20th Century Fox, FernGully: The Last Rainforest.
Both are the spirits of destruction.
Both are able to breathe fire.
Both are monstrous, violent, scary, uncaring, destructive, tempermental, bloodthirsty, dangerous, chaotic, and powerful.
The Firebird is probably the tallest, and one of the most powerful and dangerous Disney Villains, because he is totally covered by magma and lava.
Speaking of Disney Villains, The Firebird is quite similar to Te Kā from Disney's 2016 computer-animated film, Moana; then again, since they are volcanic deities of pure destruction, this comes as no surprise.
Despite only appearing in The Firebird Suite, the Firebird is considered to be the main antagonist of the entire film.
If anyone looks closely while the Firebird's awakening, anyone can see evil spirits, demons, and lost souls swarming around.
He is the only character from Igor Stravinsky's ballet to appear in the segment. However, his interpretation in Fantasia 2000, actually conflicts with the original version of Igor Stravinsky's ballet. In it, he was described as a benevolent, peaceful, and caring being who bore no traits of evil. However, Disney's version was violent, destructive, and merciless, showing no qualms of destroying a newly created forest.
The Firebird's defeat is similar to Chernabog from Fantasia; when the segment ended, they were both sent back to the ground from which they came.
However, the difference, while Chernabog was sent back from which he came by force, the Firebird merely returned by his own terms given that after the destruction that he has done, he was deprived with things that he can destroy.