Orwell does a great job with the character of Winston. The reason I say that is because Winston is so relatable. He's an "average Joe." He's 39 and has an office job. He smokes. He drinks. He has a gross itchy ulcer. He doesn't exactly scream hero type. Of course that's a standard hero introduction motif: introduce them as boring and mundane (Luke Skywalker, Harry Potter, Peter Parker, etc.) -- all "nerds." Winston fits the bill.
Orwell lets the reader know that Winston, beyond his physical profile, is a critical thinker. Right from the start, Winston questions why Big Brother is what he is and why certain rules exist. This kind of questioning of authority is what makes Winston's slow transformation to rebellious hero more believable. He starts with small infractions. He buys a journal. He then ups the ante by writing down his anti-party feelings. Next is his illicit affair with Julia.
Normally, by this point a hero character would be gaining confidence in his/her abilities, but that is not the case with Winston. He becomes more paranoid and convinced that he and Julia will be caught. On one hand this leads him to be more bold. On the other hand, it also makes him more careless, because he believes he'll be caught no matter what. Either way, Winston gets caught. He is then tortured and brainwashed into being a full-fledged party supporter. He is broken. Orwell shows the reader how an everyday man could be turned into a hero, and then completely broken within the confines of a totalitarian society.