Mr. X is the main antagonist and final boss of the Streets of Rage video game series. In all games, he is depicted as an enigmatic crimelord.
In the first game, Mr. X's criminal organization has taken over the city and the police force. Though he enlisted powerful crooks such as Boomer, Zamza, Abadede, Big Ben, and Mona & Lisa, he did not do anything to stop Axel Stone, Adam Hunter, and Blaze Fielding's efforts to defeat his organization and foil his plans. After the three defeated all of Mr. X's henchmen, they went to his lair and defeated him in a final showdown. Before the showdown, he asked the three if they wanted to join him, but they refused, knowing what was right. The good ending shows Mr. X knocked out by Axel, Adam, and Blaze and then shows the trio enjoying the peaceful city they have created by defeating Mr. X. There is also a bad ending. In order to see the bad ending, you have to make it to the end of the final round with two players. When he asks you if you want to join him, one player must answer yes with the other answering no. The one that answered yes must then prove his/her loyalty by defeating their partner. After this, the player must refuse Mr. X's final offer and defeat him alone. The bad ending shows the player becoming the new leader of Mr. X's criminal organization.
After being defeated in the first game, Mr. X plots revenge against the heroes by kidnapping Adam. Fortunately, Axel and Blaze find help by teaming up with Adam's younger brother Eddie "Skate" Hunter and a wrestler named Max "Thunder" Hatchett. After making it to Mr. X's lair, the four heroes must fight Mr. X's right-hand man Shiva before taking on Mr. X. Unlike the first and third game, there is only one good ending, where Mr. X is once again defeated and Adam Hunter is freed.
Mr. X returns once more and plans to replace official leaders with robots(in the original Japanese version, Mr. X's plan involved an explosive substance known as Rakushin). He carries his plan out with both new and old henchmen as well as a scientist named Dr. Dahm. Adam sets off to diffuse bombs that have been planted throughout the city while Axel, Blaze, and Skate team up with a cyborg scientist named Dr. Gilbert Zan, who knows a lot about Mr. X's plans and how to foil them. The team know things are more serious than they've ever been after they defeat a robotic duplicate of Axel. There are four possible endings. The worst ending occurs if you play the game in Easy Mode. While the Japanese version enables you to play through all seven levels on Easy Mode, the American version of Easy Mode ends at the fifth level after the boss fight against Mr. X's robotic imposter Robo-X. The ending has Robo-X taunt the player and encourage him/her to play through the game on a harder difficulty, claiming that they need to do better than that to defeat Mr. X. The second bad ending occurs when you fail to save the general in the sixth stage. This results in playing an alternate stage 7 where Shiva is the final boss. After defeating Shiva, Zan vows that he will find and destory Mr. X. The regular stage 7 has Dr. Dahm appear in a sub-boss fight before finally confronting the real Mr. X. Having barely survived his first two defeats, Mr. X is now a brain in a jar that fights by controlling a robot named Robot Y, known as Neo X in the Japanese version. The third bad ending plays if you save the general in stage 6, but run out of time when you defeat Robot Y. The ending has Robot Y destroy the jar containing Mr. X's brain. Before dying, Mr. X detonates the bombs planted all over the city. Adam manages to save the heroes, but their reputation has now been severely damaged, as the bombs they failed to diffuse have destroyed buildings and killed many innocent civilians. In order to get the good ending, you have to save the general in stage 6 and defeat Robot Y before the time runs out. Doing so reveals the one good ending. While Mr. X meets his end like in the previously mentioned ending, Adam now has succeeded in diffusing all of the bombs before rescuing the four heores. It is then revealed that after Mr. X's headquarters was destroyed, the heroes all went their separate ways now that Mr. X was no longer around to terrorize anyone.
Due to being killed in Streets Of Rage 3, it is unlikely that Mr. X will return if a fourth game is made. However, this does not mean he is entirely out of the question. There are at least two ways Mr. X can be brought back if a Streets Of Rage 4 is made. One is that Mr. X may not have been killed at all and that the brain fought in the previous game was a phony and that the real Mr. X is still in his body. Another way Mr. X can be brought back is that a new criminal named Mr. X could appear, like in the Streets of Rage comic featured in Sonic The Comic.
In the three-part Streets of Rage serial in Sonic The Comic, it is revealed that the original Mr. X was killed after failing to terminate Axel, Blaze, and Max, and that a new Mr. X has taken his place. The serial ended with a cliffhanger ending where the new Mr. X promised to "recoup his losses" by killing the heroes.