Quirks

Quirks are what make a character unique and interesting. One character always fondles his hamster and talks to it. One character is always annoyed when people don't fear him. One character is always fascinated with things she shouldn't be.

These add personality, and echo real life. How many people do you know that always use one word in conversation (like, um, so you see, of course), or repeatedly mention their pet even when it has nothing to do with the conversation?

Familiarity is a factor here. We pick up on the habits, and like them. After all, if you can't remember the name you go "the guy with the hamster", right? It's not their defining attribute, but it says a lot about them.

Example: Wolverine calls people "bub", and refers to himself in third person. We're used to it, he's been doing it so long. And it's a defining part of his character, that and an odd hairstyle and the whole "claws" thing.