When Walt Disney first produced Fantasia (1940), he envisioned a project that would be constantly renewed, updated, and released with new segments of animation set to classical music. Fantasia, in concept, was to be an ongoing film series that always presented audiences with something new. Unfortunately, the first Fantasia proved to be too much ahead of its time, and audiences stayed away. The film lost money, and Disney was forced to drop the project -- though the studio did release a series of “package films” throughout the 1940s which carried on the spirit of Fantasia, albeit with then-contemporary music (mostly jazz) instead of classical. As the decades went on, however, Fantasia found an ever-growing audience and eventually became one of the most successful films in movie history. A sequel was finally released in 1999: Fantasia 2000.
The original Fantasia ends on a dramatic and somber note, with the famous “Night On Bald Mountain/Ave Maria” sequence. Fantasia 2000 wraps up on an equally dramatic note, though with a decidedly more "upbeat" finale than its predecessor. "The Firebird," based on the music of Igor Stravinsky, depicts a forest sprite, an elk, and the "firebird" itself caught up in a powerful cycle of birth, destruction, and rebirth. The Disney artists based the setting and backgrounds on the 1980 eruption of the Mount St. Helens volcano. An impressive achievement of traditional and effects animation, the firebird is imagined as a ruthless, pitiless lava creature spawned by the volcano.
Fantasia 2000 was designed for and released in IMAX theaters, and then was later adapted for conventional movie screens. Due to the fact that it was produced prior to the year 2000, and many of its sequences and technologies influenced Disney artists long before the film was seen by the general public, some people consider Fantasia 2000-- and "The Firebird" -- the finale of the Disney Renaissance of the 1990s.
A related note: In 1977, animator Bruno Bozzetto released the movie Allegro Non Troppo (Not So Fast), a Fantasia parody/tribute. Allegro Non Troppo also has a Stravinsky "Firebird" segment, this one based on the story of Adam and Eve and the serpent in the Garden of Eden. Instead of Eve eating the apple, the serpent swallows it, after which he evolves into a four-legged creature subjected to ever-increasing horrors of Western civilization.