Hermione Granger is Harry's 'other' best friend. She starts Hogwarts in the same year as Harry, is in the same house, and generally shares his adventures and misadventures at Hogwarts. A teacher's pet, she is insufferably clever and hard working and always tops her grade in exams. Her catchphrase is 'Honestly, am I the only person who's ever bothered to read Hogwarts, A History?'
She first appears in the first book as an old grandmother type figure who bossess Neville around while trying to help him find his toad at the same time. While she later becomes Harry's friend, she is at first annoying, smugly self-confident, studious, and totally insufferable. I suppose some things never change...
Ahem. Anyway, Hermione. Oh yes, she is the daughter of two Muggle-dentists and has rather oversized front teeth (although that gets fixed up in book 4 - see chapter 23). On top of this, she also has extremely bushy brown hair and is often referred to (somewhat deprecatingly) by Malfoy as a 'Mudblood'. Her worst fear is Professor McGonagell telling her that she failed every subject, and in her third year at Hogwarts she elects to do every subject (and runs herself into the ground in the process). In her fourth year she begins a radical reform movement known to the world as SPEW (Society for the Promotion of Elfish Welfare) which only succeeds in offending those it's aimed at freeing (i.e: house elves) and becomes the envy of all the other girls (and boys) in Hogwarts by becoming Victor Krum's date in the Yule Ball).
By the way, her name is pronounced Her-my-oh-knee. And she hates Rita Skeeter.
Did I leave anything out? She spends more time in the library than she does in bed, is generally quite a brilliant student and is (annoyingly) usually right. She also owns a cat named Crookshanks, which Sirius describes as being 'the most intelligent of his kind'. So I guess Crookshanks and Hermione make a pretty good pair. Crookshanks is largely ignored in Book 4, though - I suppose because of Hermione's new found obsession with House Elves and Rita Skeeter (and a lack of anything for him to chase).
Oh yeah and... um, I think that's about all.