Mr. Satan (ミスター・サタン Misutā Satan) is a recurring character in Dragon Ball, voiced in Japanese by Daisuke Gōri (until 2010), Unshō Ishizuka (afterwards) and by Chris Rager in English. He is the reigning World Martial Arts Champion in Dragon Ball Z and Dragon Ball Super.
Mr. Satan first became World Champion when the World Martial Arts Tournament was revived several years after Goku won it against Piccolo. While he legitimately won it the first time, Goku and friends hadn't competed and his opponents were all ordinary people like himself who didn't know how to fly or use ki. In the Tournament Goku and friends did compete in he was only able to retain his title because Android 18, his opponent in the finals, bribed/blackmailed him for money to allow him to keep the fame which she had no interest in. Since then Mr. Satan became friends with Majin Buu, and has an arrangement with Buu to have him knock out the other fighters in the tournament and then, much like 18, fake a loss in the finals. In exchange Mr. Satan gives Buu treats and takes care of him.
He was given credit for defeating Cell in The Cell Games but he was actually defeated by Gohan. He later also claims credit for defeating Majin Buu, though he did legitimately help gather energy for Goku's Spirit Bomb when the human race wouldn't listen to Goku or Vegeta asking for help. In Dragon Ball Super Mr. Satan gives Goku money he had been awarded for defeating Buu, as he felt guilty keeping it for himself. He initially offered it to Vegeta, but Vegeta has no interest in money and is already married into the wealthiest family on Earth anyway. Goku accepts the money but only after Goten suggests the Chi-Chi might let him stop working on the farm for a while and train instead.
Mr. Satan was called "Hercule" in the FUNimation dubs of Dragon Ball Z for obvious reasons. Since Dragon Ball Z Kai however, he has been correctly called Mr. Satan like in the original Japanese version. The name "Mr. Satan" isn't his real name, he was called that after the dojo "Satan Castle" he originally trained at and he now uses it as a stage name. His real name is Mark (マーク Māku), though that was only revealed in an interview with series creator Akira Toriyama.
He is a playable character in several Dragon Ball fighting games, usually utilizing a jetpack to fly and using explosives like dynamite against his opponents.
In several games there is a Cell Games mode, which features the ability to play through a tournament ladder as Mr. Satan, complete with commentary from the man himself, ending with him defeating Cell.