Moira McTaggert is a very important figurehead in the scientific community. She is one of the leading authorities on genetic research.She won the Nobel Prize for her work in this field. She is also the longtime friend and former fiance of Xavier, whom she met when they were both graduate students at Oxford University. She is the head of her clan in Scotland and hier of Lord Kinross.Lastly, she owns a small isle in the North of Scotland called Muir Island where her research center I located. There she used to have high security cells were extremely dangerous mutants could be held for study. Logically, the whole island is under great control. The cliffs to one side is the only weak point in the security of the island.

Moira was coerced into marrying Joe McTaggert, a handsome officer who beat her often behind closed doors. After spending some time in the hospital, raped and beaten by Joe, she decided to abandon him. He refused to divorce her, finding it useful to have a wife with a Nobel for his political career, though he didn't care enough for her to try to persuade her o stay.

Moira's son Kevin was born without Joe even knowing about it. Kevin was an enormously powerful mutant, so powerful that his body was not able to contain the enormous energy inside. Moira had to lock him in a pressured cell to keep him alive. There is where he spent his childhood. Somehow, Kevin, also called Mutant Alpha and Proteus, escaped. He hen consumed his own body with his enormous power,a nd had to comsume body after body to keep alive while he searched for his father. His father did not heed Moira's advice and spurned both her and their son. In his rage and eagerness to avenge his mother and himself, he consumed his father's body. On the downside, Kevin also absorbed his father's views on his mother and mutants. His power to alter reality seriously undermined the X-Men, and almost drove Wolverine insane, while turning Edinburgh into a place of horror and despair. The only thing able to destroy the boy was iron, and since he was too mad and dangerous to be kept alive, Colossus used his metallic form to disperse his energy matrix, killing him. A grieving mother kept his son's corpse for a time, trying to revive him, but Banshee, her then boyfriend, finally helped her to let go.

Moira adopted young Rahne Sinclair, an orphan girl who was being raised by the priest of the land, but her mutant power of turning into a wolf made them believe she was possessed by the devil. After rescuing her from a mob, Moira sent her to Xavier, to teach her how to deal with her ability.

Moira agreed to spend some time in the Xavier's mansion to help him with the new X Men, and there she met Banshee, having a relationship with him for a very long time. After he lost his sonic scream, they both went to Muir Island, joining Siryn and Multipleman. During the mutant massacre, the injured Morlocks were taken there, along with Kitty Pryde and Nightcrawler. The mutants on Muir Island then formed the team Excalibur, shortly before the deaths of the X-Men in Dallas, Texas.

The Shadow King came to Muir Island, taking control of all the inhabitants. Then, he inhabited Moira and tried to kill Sean. They were freed from his control, but the bond between them began to freezes, after Sean the last one to learn she has the Legacy virus. The main cause of Moira's distress (Before the Legacy virus, of course) was that she had played with Magneto's DNA when he was a child in her care, trying to improve him, resulting in a malfunction of his genetic structure. When Magneto discovered that, he wanted to torture her, but forgave her before his supposed death. Moira, however, wasn't able to forgive herself and walked away from her beloved ones.

Moira was not used to leaving the island very often, except to help Xavier (She once was kidnapped by Arcade as well). But now that she has discovered that she is the first human infected with the Legacy Virus, she never gets out. She is helped in her research for a cure by a brilliant scientist, Rory Campbell. She feels that she contracted the Legacy virus one of two ways: either from her part in Illyana's autopsy (who died from the virus) or from her genes (her mother was a mutant). Her island, under her blessing, has been as well a base for Excalibur for a long time now.