The sumo wrestler was the disguise of Mr. Fuji.
Physical appearance[]
The sumo was an obese man with black hair tied to a bun, he wore a black mawashi and was equipped with a hypnotist ring.
Personality[]
He was notoriously evil and enjoyed the torment he was giving Mystery Inc. in ruining them.
History[]
Scooby-Doo! World of Mystery[]
He showed up out of nowhere with another Sumo wrestler who was under hypnosis and was using the hypnotist ring on the gang. Commanding that they should can call the authorities, and then wake up all the nearby civilians that he put under a hypnotic sleep to make the gang look insane over what they saw.
Noticing that they're all strong minded at resisting the effect, he commanded his sumo slave, Mikos, in telling them to keep them in place. However, he was unaware of Scooby's immunity to hypnosis and the dog walked in from of him, causing him to trip over and land right on Mikos.
Do-what-i-say unmasked.
He was then revealed to be Mr. Fuji, aka Mr. Do-what-i-say in a padded costume, a hypnotist the gang met who invited them to Tokyo. He was trying to get revenge on them for getting his uncle arrested for the unknown crime he committed by making them look insane to the authorities.