O'Brien is a mysterious, powerful, and high-ranking despot of the Inner Party, the absolute ruler of Oceania. In the early parts of the novel, he is imagined by Winston as part of the legendary secret organization, the Brotherhood, and a hope for rebellion. With his large and reassuring physique, and the antique elegance with which he puts on his glasses, he draws Winston into a philosophical bond. Yet, O'Brien's real duty is to trap and identify rebels and crush them with torture in the dungeons of the Ministry of Love, turning them back into an inseparable cell of the Party. O'Brien not only deceived Winston; he observed him silently for 7 years, studied his psychology, and offered him a false salvation in a language Winston would fully understand. In the dungeons, even while inflicting physical pain on Winston by dismantling his thoughts, he does not lose Winston's respect. He is a terrifying master of Doublethink as he explains that power is sought for its own sake and that the future is a boot stamping on a human face forever.
O'Brien's past and how he is integrated so tightly into the Party is a secret. Other than his interest in Emmanuel Goldstein, his talent for deception in having partially written the book attributed to him in his own words, and the fact that he is a massive ideologue/executioner who has overcome mental dilemmas (Doublethink) to make the Party's power eternal, there is nothing in the text about his civil past.
A large-bodied, sturdy, thick-necked Inner Party member of about forty-eight to fifty years old, with a blunt, ugly face that nevertheless has a surprisingly civilized air. His glasses give him an intellectual nobility and seriousness reminiscent of eighteenth-century aristocrats. In the torture rooms, he looks older and more terrifying with his sagging, baggy facial skin and exhausted state.
Julia
For O'Brien, Julia is merely a simple, rebellious puppet lacking philosophical depth to reach the target.
Winston Smith
O'Brien observed him for seven years, lured him into the net, and stripped his mind away inch by inch; he became both Winston's nightmare and a twisted companion who gave him proof of existence through pain.