Hercule being renamed Mr. Satan in the Dragon Ball anime is really a correction, not a change. Introduced in Dragon Ball Z’s Cell Saga, Mr. Satan is the world martial arts champion – and one of the weakest characters on the show. Though he’s believed by the public to be the great hero who defended the Earth from Perfect Cell, he’s actually just a well-trained martial artist. He doesn’t possess the massive strength, the power of flight, or any of the other abilities shared by the Z-Warriors.
Despite the fact he can’t compete with any of the heroes, Mr. Satan is actually an important supporting character. Years after fooling everyone into believing that he killed Cell, his connection to the Z-Warriors was strengthened by the introduction of his daughter, Videl, and her growing feelings for Gohan. There’s also his friendship with the good version of Majin Buu. He was kind to Buu in Dragon Ball Z, and now the two are inseparable. Mr. Satan being the only person who can keep Buu in line kept him relevant to portions of Dragon Ball Super.
For years, much of the Dragon Ball fandom knew this character as Hercule. That was what he was called in Dragon Ball Z, the merchandise associated with it, and dozens of video games where he was available as a playable character. All that changed in Dragon Ball Z Kai, the remastered version of the show. In Kai, there was no mention of “Hercule” and instead, he was called “Mr. Satan”. This was repeated in Dragon Ball Super.
That’s because Mr. Satan was always his name. He was created as Mr. Satan when Dragon Ball Z’s Cell Saga began airing in Japan, and his daughter was given the name “Videl”, which was an anagram of “Devil”. Funimation, the company in charge of making the show’s English dub, changed “Mr. Satan” to “Hercule” ahead of its release in the United States, likely due to the name’s religious significance to Americans. Since this was the name Western viewers became accustomed to, it was reused in video games as well, because calling him “Mr. Satan” would of course have caused confusion. That being said, the “Hercule” name did get abandoned eventually. Dragon Ball Z Kai, being a show that was essentially an uncut version of Dragon Ball Z, restored the character’s original Japanese name. Afterward, Dragon Ball Super followed its example and called him “Mr. Satan” as well.
Interestingly, remarks from Dragon Ball creator Akira Toriyama have revealed that neither is his real name. Though this has never been said in any of the canon installments, Toriyama has claimed that “Mr. Satan” is really just a stage name for his fighting career [via ComicBook] and the character’s actual name is “Mark”. Given that this is a little-known fact, it’s hard to imagine that ever catching on. He’ll remain Mr. Satan, but since he was known by his Funimation name for so many years, to some, he may always be Hercule. For that reason, “Mr. Satan” and “Hercule” are now used interchangeably by the Dragon Ball fanbase.