Mastermind appeared in the original Neoquest. In it, he corrupted Jahbal, using him as a puppet to infiltrate the Circle of Twelve and bring the world to its knees. When Jahbal was defeated, Mastermind revealed himself. He was defeated by the Neoquest Hero, turning to ash. However, in the Insane version of the game, it was revealed that Mastermind himself was a minion of the true evil force, Jahbal's fellow Circle member, Xantan.
I never thought that you would defeat my puppet, Jahbal, but it seems you have. You will not foil my plan to conquer the world, you fool!
Mastermind only appears in the Evil and Insane versions of the game.