What role does big brother play within the novel? What effect does he have on Winston? Is Winston's obsession with big brother fundamentally similar to or different from his obsession with O'brien?

Big Brother takes care of law enforcement, spying, and information collection. He sees all and records all!

Winston actually questions the existence of Big Brother, but he has no feelings about him (it) because Big Brother invokes no worry or fear in him. This obsession is completely different than his feelings for O'Brien who he completely adores and believes he loves.