Who is O'Brien in 1984?

O'Brien is a member of the Inner Party. He is a large, burly, and brutal-looking man, and yet Winston thinks he has a certain charm and civility. Winston suspects he is very intelligent and may share his subversive views of society. When O'Brien reveals that he does have revolutionary thoughts, Winston is excited to go with him to a secret underground meeting led by Emmanuel Goldstein. The group aims to overthrow the Party. Winston does not realize that O'Brien is secretly loyal to the Inner Party and that the secret underground group is simply a set-up by the Party to detect potential subversives. O'Brien betrays Winston and becomes his interrogator and torturer. It is he who reveals to Winston that the true, ugly purpose of the Party is to stay in power for power's sake. Like the Party, O'Brien cares for one thing only: power. He has no personal ambition, however. He only needs and wants to be a part of the Party's power structure.

As a torturer, O'Brien reveals himself to be extremely intelligent and sophisticated. His relationship with Winston is complicated and twisted. O'Brien seems to respect Winston, and he enjoys their conversations because Winston is a challenge. O'Brien and Winston ought to hate each other; after all, it's O'Brien's job to brainwash Winston and thereby destroy him. Still, they are drawn to each other out of respect and mutual understanding.