Ironically, Mojo Jojo is responsible for creating the Powerpuff Girls. He was a lab assistant named Jojo, working for Professor John Utonium when he caused the professor to accidentally add Chemical X to his formula of sugar and spice and everything nice. This accident created the Powerpuff Girls, but it also caused Jojo's brain to grow huge, turning him into the evil Mojo Jojo. He must wear a special reinforced glass dome hat over his gigantic brain.
Mojo Jojo speaks English with a Japanese accent. He has a bad habit of repeating, reiterating, and re-phrasing the same sentences over and over, continuously. He gets this speech pattern from a humorous interpretation of dialogue that is dubbed, probably from Japanese into English. It takes a longer time to say certain things in Japanese than in English. When dubbing, one wants to keep the English speaker's mouth moving for as long as the Japanese actor's mouth is moving. This can most easily be done by repeating phrases, again and again, and again. Thus a character in a Japanese movie seems to be repeating himself when listened to by English-speaking audiences. (See: Engrish)
He is disliked by other monkeys, who think he gives monkeys a bad name; when he's not doing evil things, he's also a great (and rather artistic) chef.