Gerald O'Brien was the Director of MINILUV (The Ministry of Love), which was in charge of all of the intelligence agencies in Airstrip One (England).
O'Brien plotted with Robert Kim Cherry to assassinate Sir Harold Wharton, known as "Big Brother", thereby allowing O'Brien to becoming head of Ingsoc (The English Socialist Party) in 1952. However, O'Brien was unable to maintain power and sought desperately to avoid losing his position by re-dubbing his party "New Ingsoc." Eventually, however, after documents pertaining to government irregularities and illegalities under the Big Brother regime fell into Tory hands, O'Brien was forced to reinstate the Conservative Party as an official opposition party. Soon after he was voted out of office, and most of the Ingsoc government's programs were reversed.
Shortly before being voted out of office, O'Brien's junior party members had strongly suspected that Robert Cherry and MI5 may have likely conspired together in ruining his term, including the release of the documents. Cherry, in response to the suspicions, insisted that he was innocent of this supposed conspiracy.
O'Brien may have surprisingly lived to 1969, where he is seen still supporting BB out at the Flying Cylinder.
O'Brien's attempt to reform Ingsoc into "New Ingsoc" is a reference to former British Prime Minister Tony Blair's rebranding and realigning of New Labour in the 1990s, and the "government irregularities and illegalities" possibly reflects the problems besetting the UK Government in 2006 and 2007, in particular the so-called "Cash for Honours" scandal.