The daughter of a powerful Scottish nobleman, Moira Kinross' marriage to Royal Marine Commando Joseph MacTaggert proved disastrous. Whilst studying at college, Moira met and fell in love with Charles Xavier. They became engaged, pending the annulment of Moira’s marriage, but soon after Xavier was drafted into military service. Moira promised to wait until he was released, however while he was recovering from battlefield injuries she broke off their engagement without explanation. Later, whilst in New York City, Joe MacTaggert beat and sexually assaulted Moira, causing her to be hospitalized for a week and leaving her pregnant. From then on, Moira lived apart from her husband, although he refused to grant her a divorce, and she kept the fact that he had a son secret from him for twenty years.

Moira forged a brilliant career as a leading geneticist, earning a Nobel Prize, and founded a Mutant Research Center on Muir Island off the coast of Scotland. After renewing contact with Xavier, they discussed the possibility of establishing a school for training mutants. Moira became Xavier’s silent partner in founding the Xavier Institute for Gifted Youngsters and its’ first team of mutant students, the X-Men.

When Moira’s son Kevin began to manifest destructive superhuman mutant powers, she attempted to “cure” him, but her efforts were in vain and she was forced to keep him imprisoned. Moira also came to take a young mutant Scottish girl named Rahne Sinclair as her ward, sending her to study at Xavier’s as a member of the New Mutants.

Moira finally met the X-Men while claiming to be their new housekeeper, but they soon learned her true profession. During her affiliation with the X-Men, Moira fell in love with Sean Cassidy. Meanwhile, Kevin escaped Muir Isle and began to possess the bodies of others, draining their life energies to power his ability to warp perceptions of reality. As Proteus, Kevin terrorized the town of Edinburgh and was confronted by the X-Men. Kevin attacked and possessed his father’s body, killing him, before being killed himself by Colossus.

Moira eventually became the first human to contract the mutant-killing Legacy Virus. Affiliating herself with the British super-team Excalibur, she dedicated herself to finding a cure for the Virus and eventually found one just as the mutant terrorist Mystique and her Brotherhood of Mutants attacked Muir Island. Moira was mortally wounded in the resultant destruction of her Research Center, but she clung on to life just long enough to contact Xavier telepathically and transfer the cure to him. The Beast then created an antidote from Moira’s research, which was released when Colossus sacrificed his life to disperse the cure into Earth’s atmosphere.