Gouji Rokkaku is the main antagonist in the Jet Set Radio series.
In the first game series, Rokkaku searches for a record called the Devil's Contract, which is said to summon a demon, so he can make a contract with the demon and rule the world, and kidnaps Coin to get it but fails due to the GGs interference. He was presumed dead by the GGs as his building was destroyed during the battle. Rokakku however was revealed to survive the explosion and is still well.
In Jet Radio Future, Gouji Rokkaku is the chairman of the Rokkaku group, a business organization and take over several districts in Tokyo and Rokkaku eventually becomes mayor. At his new position, Rokkaku eliminated freedom of speech and oppresses the citizens of Tokyo. He makes his branch of police officers known as the Rokkaku Police to arrest those that try to express themselves.
After the GGs defeated the police force, Rokkaku kidnapped Professor DJ and broadcasts a signal to the city to meet in the Shibuya Terminal while playing a creepy music. He tells them wipe their smiles off their face and absorbs them in the tower. Rokkaku eventually turns into a giant monster and fights the GGs. The GGs managed to take him down and destroys the Rokkaku's tower. Rokkaku dies in the explosion presumbly once and for all.