Baymax is a robotic synthformer created by the young genius Hiro Takachiho when Hiro lost his father Tomeo Takachiho. Baymax was seemingly built to be just a bodyguard but soon helped fill the void left by his father's death, certainly helped by the fact that Hiro installed many of his father's memories and emotions into Baymax's core programming. When Hiro was drafted into the Japanese hero group, Big Hero 6, Baymax came along for the ride. Hiro reluctantly joined to prevent Everwraith from slaughtering millions in downtown Tokyo. During the battle, Big Hero 6 was joined by Sunfire, Japan's premiere super hero and a mutant with the ability to super-heat matter into plasma, who was instrumental in the Everwraith's defeat.
Soon after, Big Hero 6 moved their headquarters from the Giri Office Building to Japan's Cool World Amusement Park, where they were attacked by X the Unknowable, a monster born from a child's drawings that could transform its atomic structure into any form and shape. With the help of Alpha Flight, Big Hero 6 destroyed X the Unknowable in the fires of Mount Fuji. Afterwards, Big Hero 6 continued to protect Japan from all threats, such as when the team rescued Tokyo residents from a freak blizzard caused by the Crimson Cowl (Justine Hammer) and her Masters of Evil.
The members of Big Hero 6 fell victim to a mind-control device implanted within Baymax. Traveling to Canada, the mind-controlled super heroes attacked a new incarnation of Alpha Flight at a national park. After a brief battle, the mind-control device was short-circuited and the two teams parted as friends. Big Hero 6 returned to Japan to seek out the parties responsible for their mind-control.
Big Hero 6 help Alpha Flight protect the timestream.
Spider-Man rallies many of earth heroes including Big Hero 6 to help stop the construction of Doctor Octopus' satellites.  Big Hero 6 found one of the facilities, discovered that it is guarded by Everwraith. Despite a tough battle, Big Hero 6 finally ended up victorious.
Robotic Body: Baymax is an artificial synthformer with the ability to shift into various battle forms. His default form is a large humanoid male designed to be less conspicuous in public while attending to Hiro's daily needs. He possesses a durable, polymantium exoskeleton resistant to most forms of small ballistics. Baymax can use water as his primary source of power for locomotion.
Battleform: Baymax in his battle form is more powerful and imposing. 
Sensors: Baymax is equipped with internal scanners and sensors able to detect and evaluate the threat posed by lifeforms in the immediate vicinity. He can also deploy remote monitors to record events from afar.
Flight Baymax feet are equipped with jet engines capable of generating a thrust sufficient to propel him at speeds up to Mach 4.
Communication: Baymax can send, receive, and intercept radio transmissions, and monitors all networks. He is linked to Hiro's personal Core Cyber-Network. When Baymax can be summoned via a communication device mounted on Hiro's wrist. Baymax is connected to Hiro's cybernetic glasses, so that everything that Hiro sees and hears while wearing the glasses is stored in Baymax's databanks.
Programmed Skills: Baymax is programmed with fighting techniques from several forms of combat. His artificial intelligence system is memory-card-based and contains thoughts and emotions of Hiro's departed father, industrialist Tomeo Takachiho.
When Baymax sustains physical injuries beyond his damage threshold, he automatically reverts to his humanoid form and becomes temporarily depowered.