Joseph MacTaggert was in the Royal Marines when he began dating at the time Moira Kinross who was studying at Oxford University. They however broke up when she met and began dating Charles Xavier. It was on a holiday to Devon when Joe got possessive over Moira and told Charles to back off. The couple left the pub after that and were soon involved in a car accident but were quickly saved by Charles. Moira broke up with Joe after that. However, Joe decided to break them up by getting into Charles' head and convincing him that he needed to serve in the armed forces before being a man worthy of Moira. She promised to wait for Charles until he was released from military service, but Joe weaseled his way back into Moira's heart once Charles was absent. Xavier received a letter from Moira breaking off their engagement without explanation and stating that she was returning to Scotland. Moira and Joe were soon married.
Joseph MacTaggert proved to be a brutal husband. Moira eventually fled from him to New York City, but Joe tracked her down, beat her and assaulted her sexually, 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. When Moira's son began to manifest destructive mutant powers, she attempted to cure him, but her efforts were in vain, and she was forced to keep him imprisoned at her Mutant Research Center.
Their son Kevin MacTaggert, who was code-named "Mutant X" but called himself Proteus, escaped from his confinement at Muir Isle and began using his powers to possess the bodies of others and drain their life energies and to warp people's perceptions of reality to terrorize the Scots countryside. The X-Men attempted to stop Proteus, and Moira warned Joseph MacTaggert about him. (At this point it had been twenty years since she had left him.) Proteus took possession of his father's body, ravaging it, and attempted to kill his mother. Instead, however, Proteus was himself apparently destroyed by the X-Man Colossus. Joseph MacTaggert died as a result of being possessed by Proteus.
- 4 appearance(s) of Joseph MacTaggert (Earth-616)
- 5 minor appearance(s) of Joseph MacTaggert (Earth-616)
- 5 mention(s) of Joseph MacTaggert (Earth-616)
- 3 image(s) of Joseph MacTaggert (Earth-616)