In George Orwell's 1984, how was O'Brien the ultimate betrayer?

In the
totalitarian, dystopian society depicted in 's , the possibility that those
with whom one comes into contact may not be what they seem is a constant risk. Such is the case
with the character . This mercurial figure crosses paths with 's , , only fleetingly during the
years that precede the beginning of 1984, and Winston is uncertain what, exactly, to make of
O'Brien. A large, burley man, O'Brien is also refined in a way that contrasts sharply with his
public appearance. Early in Orwell's story, the novel's narrator makes the following observation
regarding Winston's relationship to this seemingly authoritative figure who may be less
doctrinaire in his fealty to Party dictates than his official position demands:

"Winston had seen O'Brien perhaps a dozen times in almost as
many years. 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. Something in his face suggested it irresistibly."

That "secretly-held belief" constitutes the crux of the
matter, and to fully appreciate the importance of O'Brien in Orwell's society, it helps to
recall a real-life operation carried out by the newly installed Bolshevik regime that subverted
a legitimate revolution against a czar only to impose an even more draconian dictatorship on the
very people it had presumed to help.

Immediately upon taking control of the
major seats of Russian power, the Bolsheviks understood the need to protect themselves against
the machinations of internal and external enemies alike. The czar's secret police, then, was
replaced with the Bolshevik's version of a repressive, omniscient force, the Cheka (an acronym
for the Russian words for Extraordinary Commission for Combatting Counter-Revolution and
Speculation). The Cheka's leader, Felix Dzerzhinski, ordered the establishment of a fake
anti-Bolshevik resistance group operating in Western European capitals. This fake organization
was called "The Trust," and it successfully attracted Russian emigres eager to
assemble and conspire against the communist revolutionary movement systematically entrenching
itself in Moscow and St. Petersburg. The Trust operation was, in fact, successful at provoking
"disloyal" Russians into identifying themselves, making their eventual capture much
easier than would otherwise have been the case.

The reason for this bit of
Russian history is because Orwell modeled his autocratic society after the Communist Party of
the Soviet Union, and the O'Brien character's references to the Brotherhood serve asfor the
real-life Trust operation. In discussing the figure of Emmanuel Goldstein and his "vast
shadowy army, an underground network of conspirators dedicated to overthrowing the State,"
Orwell's narrator, and O'Brien, allow for the possibility that (A) the Brotherhood exists and
threatens the Party, and (B) the Brotherhood doesn't exist other than as an instrument of the
Party's propaganda and a means of furthering its repression. As Winston's commitment to the
Party begins to weaken, and the image of the Brotherhood holds out hope of an alternative, the
seeds are planted for the protagonist's newly conceptualized concerns about the Party's
legitimacy to develop into a full-fledged position of resistance. Winston now risks identifying
himself with subversive elements to which O'Brien has introduced him. If, as seems likely, the
Brotherhood was modeled after the Trust, then it will have served its purpose of deceiving
potential opposition movements into revealing themselves and, consequently, making themselves
vulnerable to isolation, capture, and destruction.

O'Brien's betrayal
succeeds because of his manipulation of others into revealing themselves as possible enemies of
the state and, so doing, setting themselves up for destruction.