Well... he's dead. But... (cue drum roll) that doesn't mean he's not an important character. He's not really, but that's besides the point. That is to say, I mean he is but... oh, I'll shut up now and just get on with his biopsy. I mean biography. Ahem.
Aaaaaaannnyyway, James died just a day before the Harry Potter series began, and thus has never really featured in it as James (he appears in Book three as a stag, and in Book 4 as a ghost/spirit/memory/smoke bomb/practical joke) in the series itself. Still we hear constantly about his childhood and his school days, and Harry is constantly told that he looks like him, so I suppose from that we can deduce what he looked like.
He looked like Harry (big surprise). *sigh*
And he acted like Fred and George. Kinda. He was a practical joker, but also a good student. And he was brilliant. In his fifth year, he managed an Animagus transformation and turned into a stag, Prongs, by which he was known to his friends ever since.
After he finished school, he married Lily, had Harry, and died (sniff).
And (sob) it's so saaaad. *sniffs*