"He felt deeply drawn to him, and not solely because he was intrigued by the contrast between O'Brien's urbane manner and his prize-fighter's physique. Much more it was because of a secretly held belief -- or perhaps not even a belief, merely a hope -- that O'Brien's political orthodoxy was not perfect."
― Part 1, Chapter 1
O’Brien is a member of the Party and was looked up to by Winston Smith. He pretends to be part of the rebellion by discussing to Winston about the Brotherhood, but ends up tricking him with his intelligence and honesty. He mentally brainwashes and tortures Winston to make him worship him and Big Brother.