Dr. Moira MacTaggert, more recently known as Moira X, is a fictional character appearing in American comic books published by Marvel Comics. She first appeared in The Uncanny X-Men #96 and was created by writer Chris Claremont and artist Dave Cockrum. She works as a geneticist and is an expert in mutant affairs. She is most commonly in association with the X-Men and has been a member of the Muir Island X-Men team and Excalibur.

Excalibur is a superhero group appearing in American comic books published by Marvel Comics. They are depicted as an offshoot of the X-Men, usually based in the United Kingdom. Conceived by writer Chris Claremont and artist/co-writer Alan Davis, they first appeared in Excalibur Special Edition #1 (1987), also known as Excalibur: The Sword is Drawn. Stories involving this team have featured elements of both the X-Men and Captain Britain franchises, frequently involving cross-dimensional travel.