Lady Mastermind is a supervillain appearing in American comic books published by Marvel Comics. Created by writer Chris Claremont and artist Salvador Larroca, the character first appeared as Regan Wyngarde in X-Treme X-Men #6 (December 2001).

Regan Wyngarde is the daughter of Jason Wyngarde, the original Mastermind. Her half-sisters are Martinique Jason, the second Mastermind, who now shares her codename, and the X-Men's Pixie. Like her sister and father, Regan possesses the ability to cast telepathic illusions. Although the character originally appeared as a villain, she would later have a brief stint as an X-Man, betraying the X-Men a short time after joining them.

Regan Wyngarde is one of three daughters of Jason Wyngarde, the original Mastermind. She has an intense hatred for her half-sister, Martinique (though she was the first to use their now-shared codename). She is hated by her sister for "stealing the spotlight", while she hates her sister for being a "skank", with the two of them constantly insulting each other.

Regan is involved in a plot created by Sebastian Shaw to have his revenge against Sage and gain control of the Sydney underworld. In an attempt to make Sage work for Shaw again, Regan places her in a series of illusions. However, with the assistance of Lifeguard, Sage breaks the illusion and reflect Regan's powers back against her, leaving her in a vegetative state.

Regan is one of the few mutants who retain their powers after M-Day. She is rendered comatose by scientists of the Fordyce Clinic, who intended to determine if a person could catch mutation like a disease. Regan finally awakens from her coma after her powers are temporarily hijacked by Serafina and goes on to join Rogue's strike force/field team. The team goes to Cable's island utopia of Providence to find a cure for Rogue after she is infected with Strain 88. While there the island is attacked by an ancient Shi'ar superweapon known as the Hecatomb, forcing Regan and the rest of the team to fight the psionic horror. The weapon is eventually defeated thanks to Rogue's power-absorption abilities, supercharged by Strain 88.

When Rogue's team of X-Men goes to one of Mystique's safe-houses, an intruder alarm later goes off. Initially confused by the seemingly invisible nature of their opponents, the X-Men are caught off guard when Regan drops her illusionary cloak to reveal the Marauders. Regan later fights alongside the other Marauders in Flint, Michigan, against Iceman and Cannonball, as both sides try to obtain the diaries of Destiny.

The Sisterhood approaches Regan, who is at a graveyard mourning her father. At first, Regan points her gun to Madelyne Pryor's head. When Madelyne promises to resurrect Regan's father, Regan joins - this, however, disgusts Martinique. Later in San Francisco, the Sisterhood perform a spell involving Kwannon's body and a captive Psylocke, restoring her to her original body. Later, when the Sisterhood attack the X-Men, Regan takes out Emma Frost by trapping her in an illusion and then leaving her bound and gagged in a dark room, cutting her off from her senses. While trapped, Frost unexpectedly finds what seems to be Jean Grey communicating to her, and seemingly aiding Frost. Frost becomes the first person not to fall for Regan's illusion, prompting Regan to worry. Frost savagely beats Regan, calling her a traitor to her kind.

Sometime later, Regan ends up incarcerated in the Raft. Together with Sabretooth, Mystique breaks Regan out of jail and offers her a chance to get rich. Regan encounters a young, time-displaced version of Jean Grey and attempts to awaken the Phoenix Force from within her, but is unsuccessful.