William Sean McFly Biographical information Date of birth April, 1885 Age (1885) born Age (1931) 46 Age (1955) 70 Age (1985) 100 (possibly deceased) Physical description Gender Male Hair color brown grey (1931) Eye color blue Behind-the-scenes information Played by Uncredited baby actor Voiced by Michael J. Fox (2010 video game)
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"So you're my great-grandfather. The first McFly born in America. And you peed on me."

—Marty to William

William Sean McFly (b. April 1885) was the son of Seamus McFly and Maggie McFly, the father of Arthur McFly and the paternal grandfather of George McFly. He was the first McFly born in America. William did not take to strangers until Marty McFly under the alias of "Clint Eastwood" journeyed to 1885 and stumbled across their farm.

He was seen earlier fully grown in a photo with relatives in the book A History of Hill Valley, 1850-1930 where Marty noted he was a "good-looking guy". Since William and his family were featured in the book, he might have been a prominent citizen and played a role in the growth of the town.

"Wait, that was Great Grandpa Willie! I met him when he was a baby! He peed on me."

—Marty, after just meeting an adult William

In 1931, William works for Hill Valley Mercantile Deliveries. He came to the Hill Valley High School on October 13 after hearing that Arthur had getting hitched to a "Canadian floozy." At first he disapproved of their marriage, but changed his mind upon meeting his son's wife Sylvia.

William briefly scolds Marty, thanking him to stay out of McFly family buisness. Then he pauses for a moment with a mildly bewildered look on his face, as if sensing something vaguely familiar out of him. William quickly shrugs this off and goes back about his buisness.

In 1931A, William worked for Haysville Mercantile Deliveries and was driving through what had once been Hill Valley on October 13. He pointed Marty and Doc Brown to the house of an old lady named Mary Pickford (who in truth was a time lost Edna Strickland). After Edna confesses to Marty and Doc that she destroyed Hill Valley. She's about to shoot them when William arrives to cover their escape by grabbing her and her shotgun, telling them to get away.

Behind the scenes

• In the photo from A History of Hill Valley, where a middle-aged William McFly is seen with his family, including his parents, Seamus and Maggie. Like Seamus, William is portrayed in the photo by Michael J. Fox as well. Bob Gale notes in commentary to Part III that the art department included "two Michael J. Foxes and two Lea Thompsons" in the picture ^[1].
• Coincidentally, actor Cliff Robertson portrayed a character named "William McFly" in a 1967 film.
• William is the only one of Marty McFly's direct paternal ancestors not known to have had a quarrel with someone from the Tannen family.
• What William McFly's supposed contribution may have been is not hinted at. It is possible that Marty's vice-principal at Hill Valley High School, Gerald Strickland, might not have been aware of this when he proclaimed that "no McFly ever amounted to anything in the history of Hill Valley" in 1985. This occurred in the unaltered timeline. When Marty McFly altered history from 1955 onwards, Strickland might not have said this. A likely explanation is that the McFly family picture is simply there because they were early town inhabitants, and never actually did anything noteworthy otherwise. However, it is also possible that the McFlys simply never amounted to anything only according to Strickland's personal standards", which are likely to be impossibly high.

Appearances

• Back to the Future Part III
• Back to the Future Part III novelization (birthdate)
• Back to the Future: The Game - Episode 5: OUTATIME

Notes and references