O'Brien and Winston
In the beginning of the book Winston thinks of a man named O'Brien that is an important Inner Party member a man who he thought for sure was an enemy of the party. He didn't know O'Brien yet he only knew his name but Winston was sure that O'Brien had the same independence and rebellion as he did. All throughout the book WInston thought O'Brien was on his side but further towards the end Winston became unsure of O'Brien and he realizes that O'Brien was never his friend he was really his enemy he was only acting as Winston's ideal. The hope he inspires in Winston is part of the psychological torture he experiences at the end of the book. Basically O'Brien was never Winston's friend like he had thought he was his enemy and the one who used rats that he hates against him to confess.
When Winston got taken into "Room 101" he realized what O'Brein had been talking about and it was a cage of rats that O'Brien used against Winston to have him confess and in the book he realized there was only one person that he could transfer his punishment to and that's when he shouted "Do it to Julia! Do it to Julia! I don't care what you do to her, strip her to the bones. Not me!" That's when the cage got taken away and it was all over.