Real Name: Jason Wyngarde (or at least, it was in the old comic series... I don't know if it still stands for Evolution, as Mastermind wasn't referred to by his real name...)
Mutant Power: Ability to tamper with people's memories and minds, and can also create mental illusions as a side effect of this ability
Voice Actor: Campbell Lane (also the voice of Rampage in Beast Wars)
First Appearance: "The Toad, the Witch, and the Wardrobe"
Back Story: Mastermind was a guy. In Italy. That Magneto recruited/forced to be on his new team. And... um... yeah.
Personality: Not much was revealed about Mastermind, as he only had a relatively brief part in a couple episodes. From what I can gather, he's a "bad guy", but wasn't a willing servant of Magneto- at least, at first, as he practically had to be forced into serving the Helmeted One. He seems less hesitant at his job now, though, so I don't know if he's just gotten used to his new job at Magneto's place, or if he's waiting for the right moment to turn on his "master"... He's a homebody, though. He stays at the Magneto Dome, probes some enemies' minds when needed, but otherwise pretty much keeps to himself- he doesn't go on "missions" like the rest of Magneto's team, as he's pretty weak physically.
Final Reflections: Ah, another underused character. Even though I don't know if Mastermind should've had a whole episode focused on him, he really could've used a bigger part than he had. I mean, after he was recruited, pretty much all he did was probe minds of people Magneto captured. Whee. I would've liked to see him actually engage in some kind of mind battle with the Professor or something.