It has been suggested that this article be split into Goku, Super Saiyan Goku, Super Saiyan 3 Goku and Super Saiyan God Goku. Please visit the discussion page if you want to object or support this decision.
Goku (known as Son Goku in Japan) is the main protagonist of the Dragon Ball franchise. He was created by manga author Akira Toriyama who is also known as the character designer for Dragon Quest and Chrono Trigger. The character is inspired by the character Son Wukong (otherwise known as "The Monkey King") from the story Journey to the West.
Goku was originally a Saiyan born under the name Kakarot, the son of Bardock and Gine, and was sent to Planet Earth in a Saiyan pod just moments before his homeworld, Planet Vegeta's destruction and moments before Bardock's last stand against the tyrant Frieza. Goku was found by an old man named Gohan who became the boy's adoptive grandfather. He gave him the new name of Goku, as a baby, Goku's Saiyan heritage was clear as he was violent and rambunctious but that all changed one day when Goku fell down a mountain and hit his head, giving him amnesia about his Saiyan heritage and has since then strived to become the best and the strongest martial artist alive.
Numerous iterations of Goku have been created for M.U.G.E.N by various authors, although it could be argued that two most popular versions of the iconic Dragon Ball character are the ones created by CHOUJIN and Balthazar & Cybaster.
The Necromancer's version
The Necromancer's Goku has gameplay that seems to be rather standard of many Dragon Ball Z characters. It features a large pool of Specials and a single button projectile. Despite this, Goku doesn't rely too much on projectiles, making it reasonably balanced.
While this version of Goku uses sprites from Dragon Ball Z: Super Butouden on the SNES, it plays nothing like said game, instead opting for the limited gameplay found in Tako's other characters. It can't combo, but has two Specials, both of which act like Hypers.
One of the most recognized and balanced Goku characters out there. It's interesting to note that this was originally a W.I.P by Ironmugen, but later given to CHOUJIN so he could make it into his own unique style. Son Goku was originally intended to play as a mix between Marvel vs. Capcom and Guilty Gear X, but little did CHOUJIN know that this style of character would form the basis of many future Dragon Ball characters.
CHOUJIN's second iteration of Goku rebels against Akira Toriama's logic that SSJ Goku is light years more powerful than his base form, in order to prevent it from being very overpowered. Its abilities are almost identical to what CHOUJIN's other Goku can do in Kaioken mode.
With many custom elements and huge combo ability, it shouldn't be any surprise that the power level of this Goku is over 9000. Unlike many other Goku characters, this version is not overpowered in the slightest, though some may say different when they challenge its A.I. to a fight.
SSJ Goku is a six-button character with a wide variety of original moves. Although he is the Super Saiyan version of Goku above, he is a completely independent character. SSJ Goku has been balanced despite the anime's logic suggesting that this Goku should be significantly more powerful. He comes with 8 levels of difficulty.
Supermystery's UB22 Goku has the ability to fly, transform into Super Saiyan 3 and Hyper Gogeta. The A.I. is absurdly powerful and cheap, always bombarding the player with many attacks.
The commands are very easy to use and he has a lot of 1-hit K.O. super-moves (including fast rushes that keep the enemy in a custom state and full-screen ki-blasts/Kamehamehas). The author thought the character had to be cheap in order to be accurate to the manga and the anime.
But in the latest years of his activity he also released a balanced version of Super Goku, using Shin Butouden sprites and having a gameplay that is similar to that of the Marvel vs. Capcom videogames. This version doesn't have 1-hit K.O. moves and they can be appreciated by more people because of the balanced gameplay.
Many people may have wondered at some point in their lives what would happen if Goku took steroids. Filled to the brim with infinites, this seems to be the most accurate answer.