Seamus and Maggie McFly

Seamus and Maggie McFly are fictional characters in the film Back to the Future Part III. They are distant ancestors of the protagonist Marty McFly, and though they do not realise that fact, they still offer him aid and comfort when he arrives in the past.

Seamus is played by Michael J. Fox, who also plays Marty McFly. The resemblance between the two characters highlights the fact that they are of the same family, if four generations removed. Interestingly, Maggie McFly is portrayed by Lea Thompson, who also plays Marty's mother Lorraine, even though these two characters are not blood relatives. Bob Gale and Robert Zemeckis explain that they simply did not want to make a Back to the Future movie without Thompson, but also offer an "in-universe" explanation — namely that "men are attracted to women who remind them of their mothers", so all McFly men after Seamus took wives who resemble Maggie.