Tadashi Hamada

Tadashi Hamada is Hiro Hamada's deceased older brother and a genius inventor from Big Hero 6. He took a lot of steps to build Baymax, according to Baymax's flashback. He is the brother-in-law of Hotaru Tomoe and also the paternal uncle of Jesse and James Tomoe.

Big Hero 6
Tadashi takes Hiro out of the Bot Fight event, meaning that Hiro is wasting time. In the University of Robotics, Tadashi takes him to learn about robotics. Back at home, Tadashi shows Hiro about his long-built inflatable robot Baymax. Later on, Tadashi tries to rescue Callaghan when a fire starts in the University. Trying to save Callaghan and Dr. Tomoe, Tadashi was killed off screen alongside Mrs. Tomoe, leaving his sister-in-law Hotaru Tomoe badly injured. A vigil was held outside the convention. Days later, Baymax asks how Tadashi loves Hiro so much before he died and how he built Baymax.

Hiro later learned that the fire wasn't an accident and that Callaghan had started the fire to steal the Microbots and had to blamed Tadashi and his mother-in-law Mrs. Tomoe for their own deaths, enraging Hiro, until his wife Hotaru managed to calm him down. At the film's end, Hiro along with Big Hero 6 avenge the deaths of Tadashi and Mrs. Tomoe by defeating Callaghan and later have a building built in Tadashi's honor.

Trivia

 * Tadashi is similar to Sitka as both are the older brother of the protagonist (Hiro and Kenai) and both died trying to save someone from a threat (Tadashi dies trying to save Callaghan from a fire whilst Sita dies saving Kenai and Denahi from a bear).