A Question of Character

This one is for the writers and RPG gamers out there.

What draws you to a character?

Not as far as reading, but creating. When you’re coming up with a new book, or preparing for a new campaign, what draws you? You need to create someone who’s both interesting and sympathetic enough for you to live with for a few hundred pages, or a few dozen game sessions, if not more. (Though obviously, the lines are drawn differently for everyone.) So what do you look for? What do you try to add? What must or must not be present for this to be a character you’re both comfortable and interested in writing/portraying?