A villain published by Marvel Comics. Mastermind first appeared in Uncanny X-Men #4.

Jason Wyndgarde's early life has never been revealed. He was working as a mentalist in a small circus when he was approached by the mutant leader Magneto to become part of his band of mutants known as the Brotherhood of Evil Mutants. Wyndgarde was a mutant with the ability to create realistic illusions.Wyndgarde joined with Magneto and the rest of the Brotherhood. They fought the students of Professor Charles Xavier, a group of mutants known as the X-Men. Magneto's group always met with defeat in the end.

Wyndgarde was not content with the Brotherhood, however and broke ties with joining another group bent on world domination Factor Three. When the leader of the group, Mutantmaster, is revealed to be an alien bent on the destruction of Earth, the group is forced to aid the X-Men in defeating him.

Mastermind disappeared for a time during which he was offered membership in the exclusive Hellfire Club. To prove his worth to become a member of the Inner Circle, Mastermind instigated a plan to get the X-Men member, Jean Grey to join the Inner Circle as their Black Queen or her own free will. To this end, he acquired from Emma Frost, the Hellfire Club's White Queen and a mutant telepath, a device that would allow Mastermind to project illusions into Jean Grey's mind. Unbeknownst to him, Jean Grey had been replaced by the cosmic entity known as Phoenix. Mastermind began to cast illusions that Jean Grey/Phoenix was in the 18th century with him as her true love. Eventually, through his efforts, Phoenix was seduced and became the Black Queen of the Hellfire Club.

The corruption of Phoenix however took a nasty turn causing her to become Dark Phoenix, a force of immense power and evil. Dark Phoenix broke Wyndgarde's hold on her and caused him to see the vastness of the universe. Wyndgarde's mind was unable to cope with the images and he slipped into a catatonic state.

Years later, Wyndgarde awoke from his coma and sought revenge against the X-Men for his trouble. He first caused Mariko Yashida, the fiance of Logan, the X-man Wolverine, to call off their wedding at the altar. Later, he tried to convince Cyclops, the leader of the X-Men, that his wife Madelyne Pryor was Dark Phoenix. He was discovered and defeated.

When the Legacy Virus, an illness that struck mutants, was spreading, Wyndgarde became one of its victims dying from the virus.