The Machinist: Christian Bale and John Sharian

Before Christian Bale was saving Gotham from a nuclear bomb, the Joker, and Katie Holmes' acting, he was busy shedding an ungodly amount of weight (a feat Bale would repeat in Rescue Dawn, The Fighter and any number of as-yet-unfilmed pictures) to play an incredibly distressed factory worker in Brad Anderson's 2004 psychological thriller. In the film, Bale's character, Trevor Reznik, who hasn't slept in a year, is being stalked by a creepy man of few words named Ivan (played by John Sharian), whom Trevor is convinced is out to do him harm. As it turns out, Trevor's insomnia is the lingering result of the horrible guilt he feels over a hit-and-run accident he was involved in, and Ivan is not actually a real person, but the manifestation of Trevor's own psychological torture. The film's climax features a top notch moment for Bale, in which he mutters the words "I know who you are" to Ivan (i.e. himself).