Horace Belger (simply called "Belger" except in Final Fight: Streetwise) is the mastermind of the Mad Gear Gang, hiding behind the guise of being a businessman. Though he rides around in a motorized luxurious wheelchair, some versions of the first game suggest that he only uses the wheelchair to discourage any likely adversaries from fighting him. His weapon of choice is a repeating bolt-action crossbow gun.
When first confronted by Mike Haggar, Cody and Guy, he is rapidly moving around in the chair, using Jessica as a human shield to protect himself. Before he can be damaged, he must be thrown from the chair. At the end of the battle, he was canonically killed by Cody, and knocked out of the window of his own tower to fall to his death.
Belger is depicted in later renditions as believing Metro City needs both him and Mad Gear. He tells Haggar that Mad Gear is a sanctuary for the troubled youth to escape the horrors of the city. It's uncertain how many of his underlings share his ideals: Sodom and Rolento both seem to hold to the ideal of a utopian society as reflected in their Street Fighter Alpha storylines (yet have differing opinions on how that should come about), though other members such as Edi E are in Mad Gear simply to further their own selfish desires. It's even more unclear just what his full goals really are for the city and Mad Gear: other than chaos and the subsequent shut-down of rival gangs around the city through Edi. E arresting them, Capcom has never stated exactly just what the final plan was for the group in Belger's eyes.
In Mighty Final Fight, a humorous take on the series, Belger appears as a half-man, half-machine cyborg. In this game, Jessica is stated to be a beacon of light for the city, and Belger's reasons for kidnapping her lie in the fact that he's fallen in love with her (something he reacts to with surprise). Save for the lack of tie and the addition of cyborg components, he resembles a super-deformed version of his regular self, though no longer bothering with his wheelchair. No reason is ever given as to why he is a cyborg at all, though it isn't treated as a surprising fact either. Unlike his original counterpart Belger's involvement with Mad Gear is treated as a known fact.
Belger returns as a zombie in Final Fight Revenge. He is the final opponent in the game, and is not a playable character. He is nothing more than a typical zombie in this state, lacking any of his original personality. The zombie is destroyed for good by Guy, Cody and Haggar, but manages to survive long enough to infect Guy through a bite. Guy retreats afterwards to meditate and purge himself of "the evil taint". Given that Guy appears in later games in the SF timeline (notably Final Fight 3 and Street Fighter Alpha 3), he obviously overcomes this.
Zombie Belger's gameplay revolves around him being able to stretch his limbs (similar to Dhalsim), giving him a great deal of attack range. He also has the ability to throw exploding organs, or completely explode in a rain of body parts for his hyper attack (only to raise himself from the ground a moment later). His other attacks include vomiting acid or biting the opponent.
An interesting twist to the fight with him was that as he took damage, his body parts would fall off and then be usable as weapons (his head behaved like a bowling ball). Beating the game without continuing rewards players with Zombie Belger dancing akin to the zombies in Michael Jackson's Thriller music video.