Marvel announced in October 2008 that its Marvel Animation division and the outside studio Film Roman would produce an Avengers animated TV series, titled The Avengers: Earth's Mightiest Heroes, for planned broadcast in 2010. The series started airing on Disney XD in the United States on 20 October 2010, on Teletoon in Canada on 22 October 2010 in English-language and March 2011 in French-language. The series started airing in Australia on 8 March 2011 on ABC3, where the season finale originally aired on 12 April 2011. Micro-Episodes began airing online on 15 October 2010, introducing heroes and other characters for the main series. These micro-episodes were compiled into the first five episodes of the main series. The series follows the storylines of the original comics by Stan Lee and Jack Kirby, as well as other series of the comics' run and other sources such as the Marvel Cinematic Universe. In June 2012, Marvel's Avengers Assemble was announced after the cancellation of The Avengers: Earth's Mightiest Heroes. Jeph Loeb, a producer on the series, stated that the series is intended to closely echo the tone and feel of the 2012 Avengers film.
Due to the executive decision to cancel the show and replace it with Marvel's Avengers Assemble, the second season of Avengers: Earth's Mightiest Heroes suffered numerous rewrites:
- The finale of the second season would have seen Galactus try to consume Hala instead of the Earth. The Avengers would have come to the rescue of the Kree since the Supreme Intelligence would have abandoned them.
- The episode "New Avengers" was originally going to take place after "Operation: Galactic Storm", with the New Avengers filling in for the original team because they were busy in the other side of the universe and not because they had been erased by Kang.
- "Emperor Stark" was originally going to be a more faithful adaptation of Emperor Doom, with Doctor Doom filling his role in the original story instead of Tony Stark.
- Some storylines were left unresolved, such as the Surtur plot.
- Writer Christopher Yost was also reluctant to make "Ultron Unlimited", arguing that it felt awkward to have robots impersonating the Avengers so soon after "Secret Invasion".