Originally a group of students, the team was formed for the purpose of capturing the supervillain Yokai, the man responsible for the death of their friend (and Hiro's brother) Tadashi, and bringing him to justice. Thanks to the students' high intellect, the group built specialized suits based on the individual skills of each member, transforming themselves into high-tech superheroes.
After stopping Yokai's plot to kill Alistair Krei, they enter a hiatus with no intention of reforming their team (except Fred). It isn't until a new threat arises in the form of Mr. Yama that the team reluctantly jumps back into action and unanimously agree to officially establish themselves as resident superheroes and protectors of San Fransokyo. In doing so, they look to honor Tadashi's wish to help a lot of people.
Outside of the core six members, other characters have been irregularly affiliated with the team. Some of these include Fred's butler Heathcliff, who occasionally provides transportation via the Frederickson family chopper and limo. Mini-Max—essentially a miniature version of Baymax—was created as a guardian for Fred, and was given his own super armor to aid the team when necessary. Richardson Mole briefly joined the team after discovering their identities, but he was dropped after his memory was accidentally wiped.
Over time, the team would see occasional upgrades provided by Hiro to enhance their performance. In "Mr. Sparkles Loses His Sparkle", Hiro invents Skymax, which act as a remote-controlled transportation system for Big Hero 6's armor. Though there was initially only one Skymax, five more were created by the time of "Kentucky Kaiju". "Big Problem" introduced the team to Ultra Armor—titanium reinforced battle armor meant to withstand greater amounts of damage from enemies. In terms of appearance, Ultra Armor resembles the team's original suits, albeit with a slick, silver-gray metallic surface. Upgraded versions of Ultra Armor that incorporates the color schemes of the team were introduced in "Prey Date".
In the film, Fred gave the name "Fred's Angels" to the team with his own theme song, a nod to Charlie's Angels. In "Baymax Returns", it is Fred that officially dubs them "Big Hero 6".
In the original comics, the team was comprised of Baymax, Hiro Takachiho (Hiro's Marvel counterpart), Honey Lemon, Go Go Tomago, and Marvel mutants Silver Samurai and Sunfire. After the latter two left the team, Wasabi and Fred replaced them as the team's current roster. Due to Silver Samurai and Sunfire being owned by 20th Century Fox at the time, Wasabi and Fred are introduced as the founding members of the team instead.
According to Big Hero 6's character design supervisor, Jin Kim, one of the main goals of this movie was to introduce multiracial characters to allow everyone to feel some familiarities about their own culture and introduce the world's racial diversity.