short answer, no real set format. write out your character and how you think he fits best. organization can happen afterwards and you'll eventually have a writeup on just the guy that's easy enough to post.
long answer...
thought about making one or a template, but ultimately figured that anything i'd come up with just is good for me, not necessarily for everyone else. so it's a bit of a copout - the general format is "how the character can be best represented." basically, write away. tweak accordingly. it doesn't have to be set in stone immediately and there's time to tweak, work on, and edit your entry.
some stuff you'd want to cover in there, like how's the world he's from, what can he do, how does he do it, what has he done, what special rules does his universe have that are relevant (e.g., star wars and the force), if there are any specific traits or features to him that are relevant (e.g., a special mole that seduces women *cough*). so long as you flesh things out, the format will generally come together and eventually a 'standard' that people like will be used.
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"Maybe it's a tentacle, molesting the planet itself. - Aschen Brodel.