Mastermind is the name of several fictional characters, all of whom are or have been supervillains, who exist in the Marvel Comics universe.

The original Mastermind was a mutant with the ability to generate telepathic illusions. He first appeared in X-Men volume 1 #4 as a member of Magneto's Brotherhood of Evil Mutants. He was later involved with the Hellfire Club during the famous "Dark Phoenix Saga", in which he was largely responsible for turning the Phoenix into the Dark Phoenix. During this time he used the name "Jason Wyngarde"; this may have been his real name, although some stories suggest that it was only an alias. He later interfered with the weddings of Cyclops and Madelyne Pryor and of Wolverine and Mariko Yashida ; although the former couple were subsequently married, the latter were not. Mastermind died some years later as a result of the Legacy Virus, in Uncanny X-Men Annual #17.

Another character called Mastermind, unrelated to the original, appeared during the original Captain Britain stories published by Marvel in the United Kingdom. This Mastermind was an alien artificial intelligence that had been built by Captain Britain's father, Doctor James Braddock, Senior. Mastermind lived in the Braddock family's estate until it was reprogrammed by Kang the Conqueror and subsequently destroyed.

The original Mastermind was later revealed to have two daughters who both inherited his mutant power. Martinique Jason, a brunette,first appeared in Wolverine/Gambit: Victims #2, where she teamed up with Arcade; she later joined the Brotherhood of Evil Mutants. Regan Wyngarde, a blonde, first appeared in X-Treme X-Men #9.

The different hair color and use of name initially served to confuse readers. The next appearance of Martinique in the pages of Uncanny X-Men revealed that the two are different persons. They were established as half-sisters, rival claimants to their paternal legacy. Martinique uses the codename Mastermind. Regan is now called "Lady Mastermind" to distinguish herself from her sister.

Regan is currently in a comatose state after a conflict with Sage. Martinique is still active.