Oooooh yes. The only one I've been putting effort into fleshing out is Candie Keane the Zombie Chick.. I have a million charaters, but she's the only one I came up with specifically for cosplay.
-Inspiration- To be completely honest, I wanted an interesting costume for the bar we didn't go to on Halloween this year that people would recognize as a "traditional" Halloween costume. I knew I wanted to wear a specific dress, I knew I wanted to do makeup and I new I wanted to wear Snow's curly pink wig. I ran from there. I usually take a general idea and go on a dollmaker site and use ALL the makers and see what I can come up with, what is new and what works better. She started out entirely fluorescent green, with curly cotton candy pink hair in pigtails with a giant lolipop and a black strapless dress. She's evolved into a more realistic zombie color, with actual stitches in realistic places and she wears a raspberry pink wig instead of having magic milkshake pink hair. She still wears the black dress, but she's also a lounge singer, so why the hell not?
-Backstory- After we didn't go to the bar that night, I decided she needed a place to live and friends to play with and a complete and total overhaul. Then I decided I was going to make a comic, "Finn's Comic; starring Candie Keane and Friends." I get really way too into giving characters backstories. My favorite is "this is this way because of why?" I'm still working on a plausible reason for why she's not mindless.. I may have to jam her into the Ugly Americans fandom to solve that issue and I really would rather not do that.
-Why- Characters just kind of pop into my brain and go "HERE I AM. HERE'S MY FACE, NOW DO SOMETHING WITH ME." And I pick them up, take them in and give them homes. If I don't put them on paper, they sit in my head and scream until I do. ....and that's all I have to say about that.