The most direct evidence that Big Brother is merely a figure head and not a real person, is that he never actually appears in person to anyone. He is the face that stares from the posters reminding citizens that "Big Brother is Watching!" He is all powerful, and all knowing; almost omnipotent and reminiscent of deity's from Judeo-Christian religions. He looks (remarkably) like Joseph Stalin.
Though his picture is everywhere, there is no video of him on the telescreens, he never makes speeches, he never appears in public. Instead he remains a figurehead that represents different ideas to different citizens. To the proles, he is a distant figure of authority. To the outer party he is a leader who justifies their actions and beliefs. To the inner party, he is a safety net, ensuring the compliance of the outer party and the proles. To the inner party, Big Brother is a scare tactic, a piece of propaganda, a totalitarian tool.