The Hangover is a 2009 American comedy film directed by Todd Phillips and written by Jon Lucas and Scott Moore. It is the first installment in The Hangover trilogy. The film stars Bradley Cooper, Ed Helms, Zach Galifianakis, Heather Graham, Justin Bartha, Ken Jeong, and Jeffrey Tambor. It tells the story of Phil Wenneck (Cooper), Stu Price (Helms), Alan Garner (Galifianakis), and Doug Billings (Bartha), who travel to Las Vegas for a bachelor party to celebrate Doug's impending marriage. However, Phil, Stu, and Alan wake up with Doug missing and no memory of the previous night's events, and must find the groom before the wedding can take place.

A comedy film is a film genre that emphasizes humor. These films are designed to amuse audiences and make them laugh. Films in this genre typically have a happy ending, with dark comedy being an exception to this rule. Comedy is one of the oldest genres in film, and it is derived from classical comedy in theatre. Some of the earliest silent films were slapstick comedies, which often relied on visual depictions, such as sight gags and pratfalls, so they could be enjoyed without requiring sound. To provide drama and excitement to silent movies, live music was played in sync with the action on the screen, on pianos, organs, and other instruments. When sound films became more prevalent during the 1920s, comedy films grew in popularity, as laughter could result from both burlesque situations but also from humorous dialogue.