Baymax is the deuteragonist of Disney's 2014 animated feature film Big Hero 6. He is an inflatable computerized robot created by Tadashi Hamada to serve as a personal healthcare companion. Following Tadashi's death, Baymax was inherited by Hiro Hamada, with whom he became a member of the superhero team known as Big Hero 6.
He is based on the Marvel character of the same name from the Marvel Comics Series, Big Hero 6.

Baymax was conceptualized by Tadashi as a prototype healthcare-providing robot nurse to be mass-produced, with a goal to improve healthcare around the world. He was constructed using equipment and funding courtesy of the San Fransokyo Institute of Technology. Baymax's artificial intelligence (which was based on a thesis by SFIT alumni, Wendy Wower) comes from a special chip with Tadashi's inscriptions. The chip is equipped with a caregiving matrix, and without it, Baymax can be conceived as an entirely different being. As programming would have, Baymax is instantly summoned by the sound of distress, and can only deactivate once his current patient states, "I am satisfied with my care."

A story about two brothers and a robot, Baymax.
 
Set in a fictional metropolis called San Fransokyo (a portmanteau of San Francisco and Tokyo), a young robotics prodigy named Hiro Hamada and his robot Baymax uncover a criminal plot and pull together a team of inexperienced crime-fighters, including Wasabi, Honey Lemon, GoGo Tomago, and Fred to solve the mystery surrounding the crime.
 
Note: The chapter count includes the prologue.

The adventure story revolves around Hiro, a 14-year-old boy who lost his dear brother Tadashi in a mysterious accident, and Baymax, a personal healthcare companion robot developed by Tadashi. The story is set in San Fransokyo, a fictional city that combines the imagery of San Francisco and Tokyo.

(Source: Anime News Network)