O'Brien is a fictional character and the main antagonist in George Orwell's novel Nineteen Eighty-Four. The protagonist Winston Smith, living in a dystopian society governed by the Party, feels strangely attracted to Inner Party member O'Brien. Orwell never reveals O'Brien's first name.
Winston suspects that O'Brien is secretly opposing the Party. Eventually O'Brien approaches Winston with some leading remarks which seem to confirm Winston's suspicions. Winston finds the courage to approach him candidly, declaring himself an enemy of the totalitarian state. At first, Winston's intuition seems to be correct: O'Brien presents himself as a member of the "Brotherhood" seeking to overthrow the Party.
When Winston is later arrested, it turns out that O'Brien is actually entirely loyal to the Party. He reveals himself as he enters the cell by responding to Winston's exclamation ("They've got you too!") by wryly commenting, "They got me a long time ago." This may mean that he once had rebellious feelings like Winston, or it may simply refer to him becoming involved with the totalitarian Ingsoc movement at an early stage. The point is never elaborated on again in the novel.