<P> To enroll, he signs up for the school's science fair and presents his project: microbots, swarms of tiny robots that can link together in any arrangement imaginable using a neurocranial transmitter . At the fair, Hiro declines an offer from Alistair Krei, CEO of Krei Tech, to market the microbots, and Callaghan accepts him into the school . At the end of the day, a fire breaks out among the exhibits and Tadashi rushes in to save Callaghan, the only person left inside . The building explodes moments later, killing Tadashi . </P> <P> Weeks later, a depressed Hiro inadvertently activates Baymax, the inflatable healthcare robot that Tadashi created; the two find Hiro's only remaining microbot and follow it to an abandoned warehouse . There they discover that someone has been mass - producing the microbots, and are attacked by a man wearing a Kabuki mask who is controlling them . After they escape, Hiro equips Baymax with armor and a battle chip containing various karate moves, and they track the masked man to the docks . GoGo, Wasabi, Honey Lemon, and Fred arrive, responding to a call from Baymax, and the masked man chases the group . The six escape to Fred's mansion, where they decide to form a high - tech superhero team to combat the villain . </P> <P> The group tracks the masked man, whom they suspect to be Krei, to an abandoned Krei Tech laboratory which was used for teleportation research until a test pilot was lost in an accident . The masked man attacks, but the group subdues him and knocks off his mask--revealing him to be Callaghan, who had stolen Hiro's microbots to shield himself from the explosion . Enraged, Hiro removes Baymax's healthcare chip, leaving only the battle chip, and orders him to kill Callaghan . Honey reinstalls the healthcare chip at the last second, preventing Baymax from carrying out the kill order . Callaghan escapes, and Hiro leaves with Baymax, intent on avenging Tadashi . </P> <P> Back home, Hiro tries to remove the healthcare chip again, but Baymax stops him and states that vengeance is not what Tadashi would have wanted . To calm him down, Baymax shows Hiro videos of Tadashi running numerous tests during Baymax's development as a demonstration of Tadashi's benevolence and legacy . Hiro remorsefully apologizes to his friends, who reassure him they will catch Callaghan the right way . </P>

Who was the villain in big hero 6
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