- Avengers (Only appearance)
- Nick Fury (Only appearance)
- Betty Ross (Only appearance)
- Hulk (Bruce Banner) (Only appearance)
- Bucky Barnes (Only appearance)
- Gail Barnes (Only appearance)
Races and Species:
- Earth-3488 (Only appearance)
- Vibranium (Only appearance)
- Iron Man Armor (Only appearance)
- Captain America's Shield (Only appearance)
- Mjolnir (Only appearance)
- Pym Particles (Only appearance)
- Ant-Man's Helmet (Only appearance)
- Ant-Man's Ants (Only appearance)
- Super-Soldier Serum (Only appearance)
In the last days of World War II in the European Theatre, Steve Rogers, a U.S. soldier, known as Captain America due to being enhanced with the "Super-Soldier Serum", prevents a missile launch by Nazis, which are soon revealed to be shape-shifting extraterrestrials led by one taking the form of SS officer Herr Kleiser. The missile explosion, however, knocks Rogers out and he falls into the icy waters of the North Atlantic, presumed dead. 70 years later, Captain America is found and revived by a S.H.I.E.L.D. team led by General Nick Fury. Bruce Banner and his ex-girlfriend Betty Ross lead a team of government scientists working to recreate the Super-Soldier Serum in order to try and stop the real power that backed the Nazis - the alien Chitauri. Banner thinks the Super-Soldier Serum is the key to him controlling the Hulk, and he secretly uses his blood to try to create a cure, instead of using candidates that had been selected for the rebirth procedure.
A Chitauri attack on a S.H.I.E.L.D. satellite designed to track the alien ships forces Fury's superiors to order the implementation of "Project Avenger", creating a team of superhumans. Fury tries to recruit - with mixed success - Ant-Man (a scientist who had been redacted from S.H.I.E.L.D), Wasp (Ant-Man's wife), Iron Man/Tony Stark (an industrialist playboy), Thor (whose claims to be the genuine Norse deity are not widely accepted) and Black Widow, a S.H.I.E.L.D. agent. After several setbacks, including a botched mission that led to almost the entire team quitting, the heroes unite to fight the Chitauri. Although successful, the team must then fight an out of control Hulk, after Banner tried his new serum, releasing his alter ego for the battle against the Chitauri. The team managed to eventually distract the Hulk long enough for Betty to calm him, and Banner is then incarcerated. Later they celebrate the Avengers' success.
|Justin Gross||Captain America / Steve Rogers|
|Marc Worden||Iron Man / Tony Stark|
|Andre Ware||Nick Fury|
|Grey DeLisle||Wasp / Janet Pym|
|Nolan North||Giant Man / Hank Pym|
|Olivia D'Abo||Natalia Romanov / Black Widow|
|Michael Massee||Dr. Bruce Banner|
|Nan McNamara||Dr. Betty Ross|
|James K. Ward||Herr Kleiser|
- Despite not possessing any score at Rotten Tomatoes, the movie was partially well received for the fans and critics.
- The Chitauri revealing themselves is another departure from the comic books. In the comics, they appear only in human form, except for Kleiser.
- In the comics, Hank and Janet's argument after their first mission failed led to physical abuse. In the movie, Hank just got mad and stormed off.
- Iron Man concealing his identity is another departure from the comics. In the comics, Nick Fury wants Tony Stark to join the Avengers because he is a publicly recognized "brand name", and his new Iron Man armor might be useful to S.H.I.E.L.D.
- The original idea was for Captain America to appear during the first Gulf War, not World War II. Writer Mark Miller reconsidered, and kept Captain America's origin as it was in order to provide richer story opportunities.
- In adapting the Ultimates for the screen, the filmmakers retained writer Mark Miller's choice of playing Tony Stark with an air of arrogance, making him come off more as a playboy than an engineering genius.
- In the Ultimates universe, the U.S. government put the Avengers together. However, in their original comic book incarnation, the heroes banded together on their own.
- The filmmakers chose to produce Ultimate Avengers in the traditional 2-D cell animation process as opposed to the current trend of computer generated animation. Producer Craig Kyle explained that he believed that traditional animation remains a powerful medium for conveying character emotion on screen.
- The sequence of Captain America risking his life to stop a bomb is taken right from the pages of The Ultimates #1.
- Partially based on the Marvel comic The Ultimates. The plot is a truncated version of the first two story arcs in the Volume 1 series. The characters of Thor, Hulk, and General Fury are watered down versions of the Ultimates comic book characters of the same name. Captain America, Jarvis, Wasp, Giant Man and Iron Man in this cartoon are adapted from the Avengers comic books, as well as Iron Man, Captain America, and Tales to Astonish, published from the 1960s to the early 21st century.