If you're only using the character's name, then something like the following would do
RewriteRule ^character/(.*)$ /character.php?slug=$1
with a URL of eg http://www.example.com/character/Jim_Carrey. You'll then need to look up the character's name in the database using the slug passed in, as you won't have the ID to look it up with.
Alternatively you could include the ID in the URL if you need it, vis:
RewriteRule ^character/([0-9]+)/.*$ /character.php?id=$1
This way you could have a URL like http://www.example.com/character/3/Jim_Carrey which would include the character name (for SEO reasons etc etc), but also the ID which you could then look up directly in your database.
Edit a small PHP example for you re the first one:
<?php
// ... database connection stuff here etc
$slug = $_GET["slug"];
// IMPORTANT: perform some data sanitization here
// I'm just going to make sure it's only letters, numbers and
// hyphens/underscores as an example.
$slug = preg_replace("/[^a-zA-Z0-9\-_]+/", "", $slug);
// Now look up in your database
// Ideally you'd have a slug column to compare this with, that you can fill
// when your record is created/updated
// You'd also be best off using bound parameters here, rather than directly
// adding the data into the query string. I personally use the MDB2 PEAR
// module but feel free to use whatever you normally use.
$qry = "SELECT * FROM characters WHERE slug='" . $slug . "'";
$result = mysql_query($qry, $db);
// do something based on this result, fail if none found
// or show details if OK etc
// ...
?>
Hope this helps! As always, use bound parameters where possible for your queries, and perform sanitization of your user data well. The PEAR MDB2 module has a nice page on how to do this here.
Edit 2 a quick and dirty setup :-)
.htaccess file as follows:
RewriteEngine On
RewriteRule ^character/(.*)$ /character.php?slug=$1
Your .htaccess file would ideally be in the root of your site. Eg /home/wayne/public_html/ or wherever your index file is served from
A URL to match that would be http://www.example.com/character/Jim_Carrey - with the phrase "Jim_Carrey" appearing in your $_GET array as $_GET["slug"]. NB apologies, wrote that PHP sleepy last night above so no wonder $_POST wouldn't work as its a GET request :-) I've updated it now!
Finally you need to make sure that your host supports the use of .htaccess files. The setup of this is out of the scope of SO so any Apache configuration questions you'd be best asking over at http://serverfault.com/