When creating any kind of animation it is always good to draw up your characters and give them a back story. Character designs also have things called turnarounds. This is for the when the animator makes their puppet and need to know the scale and size from all angles. Some of these characters you will recognise, but a lot only went as far as this. I tend to sketch my characters in pencil first and then when I'm happy I colour them in on photoshop with my graphics tablet.