Big Brother is the nominal leader of Oceania in Nineteen Eighty-Four, George Orwell's chilling dystopic novel. The name is now used to mean government surveillance in general.

"Big Brother" is a dictator in a totalitarian state, taken to its utmost logical consequence. In the society that Orwell describes, everybody is under complete surveillance by the authorities. The people are constantly reminded of this by the phrase "Big Brother is watching you", which is the core "truth" of the propaganda system in this state.

The physical description of "Big Brother" is reminiscent of Joseph Stalin or Horatio Kitchener, 1st Earl Kitchener of Khartoum. In the novel, it is not clear if he actually exists as a person, or is an image crafted by the state. However, since Inner Party torturist O'Brien at one point tells Winston Smith that Big Brother can never die, the implication is probably that Big Brother is merely the Party personified. In a book supposedly written by the rebel Goldstein (but later revealed to have a more complex origin) it is stated that "nobody has ever seen Big Brother. He is a face on the hoardings, a voice on the telescreen... Big Brother is the guise in which the Party chooses to exhibit itself to the world. His function is to act as a focusing point for love, fear, and reverence, emotions which are more easily felt towards an individual than towards an organisation." (See: Goldstein's book.)

In Party propaganda, however, Big Brother is presented as a real person, who was one of the founders of the Party along with Emmanuel Goldstein. His real name is never mentioned, and it is not even clear whether it is publicly known.

Since the publication of 1984, the phrase "Big Brother" has entered general usage, to describe any overly-inquisitive authority figure or attempts by government to increase surveillance. The reality TV programme Big Brother takes its name from 1984, and a similarly named figure is big mama - the informal name for the internet censor on web boards in the People's Republic of China.