Here's why:
* Winston invents him: Winston is working for the Ministry of Truth and tasked with rewriting history. He decides to invent a hero, Comrade Ogilvy, to replace an erased Party member.
* The "hero" is a fabrication: Ogilvy is a "perfect" Party member, achieving all the ideals of Ingsoc. He is described as a skilled war hero, a dedicated Party member, and someone who embodies the "spirit of the Party."
* His existence is erased: When Winston is captured by the Thought Police, he is forced to admit that he invented Ogilvy and that he doesn't exist. This illustrates the Party's control over history and the ability to erase anyone who doesn't fit their narrative.
Ogilvy's existence highlights the theme of totalitarian control and the manipulation of truth in Orwell's 1984.