During one of the depositions, it is mentioned that the invention of Facebook made Mark Zuckerberg "the biggest thing on a campus that included nineteen Nobel Laureates, fifteen Pulitzer Prize winners, two future Olympians, and a movie star." One of the lawyers then asks, "Who was the movie star?" and the response is, "Does it matter?" This movie star was, in fact, Natalie Portman, who was enrolled at Harvard from 1999 to 2003, at the same time as Mark Zuckerberg. She invited Aaron Sorkin to a dinner party with her Harvard friends to provide him insider information on the school's social life at the time Facebook was created.
Jesse Eisenberg, who is diagnosed with obsessive compulsive disorder (OCD), said in an interview that one of the hardest things about the role was having to deliberately speak and behave in a manner he had struggled against in his own personality his entire life.
Mark Zuckerberg originally planned never to see this movie. He ended up taking several of his employees to see it. He later remarked that, despite some of the film's inaccuracies, they got his clothing right.
Jesse Eisenberg and Andrew Garfield became good friends during filming. According to Eisenberg, the dramatic rivalry between their characters was hard for the two because it affected them emotionally.
After casting, David Fincher forbade principal actors from meeting their real-life counterparts until filming was completed.
Josh Pence: The man that Mark and Eduardo send away from the restroom in the night club by remarking, "Sorry man, a couple of girls are freshening up in there," is Josh Pence, who plays Tyler Winklevoss from the neck down.
Aaron Sorkin: The ad executive that Zuckerberg and Saverin meet in New York is played (in a credited appearance) by Sorkin, the screenwriter for this film.