Justin Timberlake plays Sean Parker, cofounder of Napster and a Facebook executive. It was reportedly the most difficult role to cast; Timberlake auditioned multiple times before getting the part.
Andrew Garfield plays Eduardo Saverin, cofounder of Facebook. Garfield has been cast as Peter Parker in the 2012 version of Spider-Man.
Rooney Mara plays Erica Albright, the “Helen of Troy of Facebook,” who rejected Mark Zuckerberg, causing him to create a Facebook precursor as a form of revenge. Mara has been cast as Lisbeth Salander in David Fincher’s The Girl With the Dragon Tattoo.
Jesse Eisenberg plays Facebook cofounder Mark Zuckerberg.
Armie Hammer plays twins.