Professor Robert Callaghan, or also better known by his supervillain name Yokai, is the main antagonist of Disney's 54th full-length animated feature film Big Hero 6, and a minor character in Big Hero 6: The Series. He is a former university teacher presumed dead in a fire; until he later re-emerged using a vast army of microbots in his plan to take revenge on Alistair Krei, whom he blames for the supposed death of his daughter Abigail Callaghan. He is the former arch-nemesis of Hiro Hamada and Baymax along with Big Hero 6.
The problem with him for is that he is just a generic "mystery" villain who stole Hiro's microbots for reasons that are explained later.
He keeps up Disney's tradition of having poorly-done twist villains which are very weak and forced, similar to Hans from Frozen and Bellwether from Zootopia.
Callaghan's reveal as the mastermind supervillain wearing a Kabuki mask named Yokai was pretty obvious considering he barely got any screen time in the first act, and Allistar Krei's suspicion would have given the twist away.
His reveal was also out of place coming with an attempted justification for it, to the point were he feels like a Scooby-Doo villain.
The film expects the audience to sympathize with Callaghan just because his daughter went missing, but the fact that he tried to destroy half the city for no proper reason, stole government property, and showed no pity over Tadashi's death makes it hard for us to relate with him.
He told Hiro that it was Tadashi's fault he died (which is partially true, since he did run into the fire) even though he was the one who had set the fire in anger.
Despite his name, he was never referred to as "Yokai" in the movie and is officially nicknamed "Mr Kabuki", also, his name is actually Japanese for “Ghost”, even though he doesn't have anything supernatural, although this might be intentional due to being the "mystery" character.
His plan involves using the typical sky beam which has been used to death in previous movies of the 2000s and 2010s, mostly from the first Avengers movie when Loki zap the blue sky at the top of the Empire State Building.
In the manga adaptation, he was shown to be nearly evil in that version and was the one to force Tadashi to go to the portals he invented (while the movie let him die in a fire).
As mentioned before, his tragic backstory about losing his daughter can make some people feel for him. Plus he did reform himself when he realized what he had done in the TV series of the same name while the manga adaptation did expand his backstory.
His design is kinda cool.
James Cromwell does a good job voicing him.
The real Yokai should have not been Professor Callaghan and could have if a sequel or an episode from the tv series of the same name was made.
He was going to have two thugs (a geisha and a sumo) in the deleted scenes.
YouTuber Schaffrillas Productions uses Yokai in a good amount of his Analysis Videos.