1921 was a year in the 20th century.
Behind the scenes
In commentary to Part III, Bob Gale said that he and Robert Zemeckis "toyed with the idea" of having a film sequel in which Doc and Marty go back to the "roaring '20s", where they would meet a bootlegging ancestor of Biff Tannen, Doc's mother, and other characters . Ultimately, the choice was made instead to conclude the film as a Western in 1885.
- Monday, May 16: Harry Carey, Jr. (Old timer of the Palace Saloon, Zeke) is born in Seagaus, California.
- Back to the Future Part II novelization p. 163
- Commentary Part III, at 15:30