General Ganzu is a one-eyed alien monstrosity that lay hidden until after Plasma Bomber and Bomberman's final confrontation - when Plasma Bomber tried to call a truce General Ganzu decided to reveal himself and knocked Plasma Bomber out before assaulting Bomberman personally.
Normal explosions do not reach this boss, the bombs must be picked up and thrown at him.
When the alien is dealt a fiery defeat, Bomberman blows up the area General Ganzu was at and unlike the other villains of the story he did not return in any sequels - suggesting General Ganzu was destroyed in the battle.
although largely speculation it is possible that General Ganzu was an associate of Bagura, the nemesis of Bomberman.
The Bomberman 2 manual specifies the Evil Bombers were created by aliens, perhaps he's the mind responsible.