Yesterday, Lori posted a wonderful blog on falling in love with secondary characters. They give us the liberty to explore avenues we can't take with our protagonists. You can go as crazy (and I often do) as you want and never have to see the words, "well, that's not very hero/heroine-like, is it?"
I think the reason secondary characters are not as intriguing in their own stories is because they can't be. A smooth-talking playboy who charms his way into your heart is fine for a secondary character, but as a hero, not so much. No one wants their beloved heroine saddled with a cheating cad, no matter how sweetly he talks to her.
We also wouldn't want our hero to spend his life with a conniving she-devil. Let's face it, by the end of the story that she-devil has to see the error of her ways and reform to the perfect woman or our readers will not be happy campers.
Sometimes the most fun we have is with the characters who are never meant to have their own story. Like the lovable best friend, who's (gasp) bald! (just as a side note, I think bald guys can be just as sexy as their well coiffed counterparts). Or the 50+ socialite who decks herself in diamonds and pearls, throws on a sweat suit (Gucci, of course, if they make such a thing) to go bowling.
When coming up with your secondary characters, it's important to give them as much attention as your protagonists. Sure, you won't delve as deeply into their psyche and you'll probably never reveal their favorite color, but it will make them 3-D characters and that's something we all want. We've talked about characters doing things--well--out of character before. Don't do it, or if they do, give a damn good reason.
We can dress them up like Barbie Dolls in crazy outfits and personalities. We can throw them into insane situations, even add suspense because, unlike our main characters, we can kill them off.
Unless, of course, they have want their own story :) but I won't tell if you won't *w*