The decision to pair Scarlet Witch and Wonder Man up as a couple was based upon the storyline then running in the Avengers comic in which Scarlet Witch (who in the comic had a long-standing relationship with Vision and who hated Wonder Man because of his stalker-esque obsession with her and his refusal to help restore Vision's mind after Vision had his mind erased, a decision that ultimately led to Vision dissolving his relationship with Wanda) resurrects Wonder Man to serve as her protector after an evil sorceress transforms the planet into a medival world under her control. During their time together, the two fall in love and become a couple.
In the promotional images of the series, and the action figure photos, Hawkeye didn't wear a mask. However, in the series and the final version of the figure, he wore a mask similar to the one he wore during the Avengers: The Crossing storyline.
Tentative plans for additional episodes featured: Hawkeye's return to the carnival where he grew up; an exploration of how Scarlet Witch discovered her powers; guest appearances by the X-Men, which would have utilized the Toronto-based cast from the series since Tony Daniels, Lenore Zann, and Ron Rubin had already worked on X-Men (1992); Dr. Robert Bruce Banner (a.k.a. The Incredible Hulk) appearing to help the team when Henry Pym/Ant Man fell ill to gamma radiation exposure during a fight with the Egg-Head; and a two-part episode featuring Thor and his brother Loki (there was even a Thor toy made for the show's line of action figures). However, all plans were scrapped when the show did not return for a second season.
In 1997 Roland Poindexter, the supervising executive in charge of animated series at Fox, approached X-Men (1992) animated series writers Robert N. Skir and Marty Isenberg to develop a proposal for an Avengers cartoon. After creating a detailed thirteen-episode story arc, the network decided a Captain America series would be more suited to its schedule. But before Fox could green-light either series, Marvel went into bankruptcy, effectively ending the development process for all its shows. It wasn't until after the publisher's financial woes were resolved in late 1998 that Poindexter revived interest in the Avengers project, this time approaching former X-Men series story editor Eric Lewald and his wife Julia Lewald to come on board as story editors for the series. In January 1999, Fox finally gave the official go-ahead and Ron Myrick was hired to oversee the show's visual development.
The Avengers roster for the cartoon is loosely based upon the roster for the 1984 Avengers spin-off series "The West Coast Avengers". Notably absent from the lineup are the traditional core members Captain America, Iron Man, and Thor, who were originally prohibited from appearing in the series due to licensing issues. Story editor Eric Lewald has commented on their absence and had said "We want this to be a team of Avengers, instead of making it 'Captain America and the Avengers' or 'Thor and the Avengers.' We prefer to have a balanced team of superheroes rather than a superstar on the team." Captain America and Iron Man each made one guest appearance (in "Comand Decision" and "Shooting Stars", respectively). Thor did not appear; plans for a story arc involving him meant for the second season were dropped when the show was canceled after one season.
This series, along with Spider-Man Unlimited (1999), was commissioned by Fox in the wake of the success of Batman Beyond (1999). In order to attempt to emulate "Batman Beyond", changes were made to the Avengers franchise as the series was set in the future. Ron Myrick explained that they were "setting the series about twenty-five years in the future" and that "New York City will be a mix of future and contemporary looks, sort of the way the city looked in the movie Blade Runner (1982) but not as dark". The Avengers were also featured wearing elaborate armor costumes when they went into battle. Myrick said "The armor will give them the capability to go into different environments like extreme heat or cold, or underwater, or outer space, and it'll enhance their abilities." The Avengers also featured an "A" on their costumes that was like a Star Trek com-link, where they could hit it and communicate with each other and the mansion's computer.