As an author who is also an illustrator, I love drawing my characters as I work on a book. It helps my writing when I'm trying to describe what my characters look like, not to mention it’s a lot of fun. If you are a writer who is not an artist, try finding pictures of people in catalogs that are as close as possible to what you picture in your head. You can refer to them from time to time and it will help to get the creative juices flowing. My characters often change as I write. The sketch of the main character from my Mermaid of Windwaithe Island book started off older then she ended up, which is why she looks a lot older in the picture than she is in the book. My protagonist’s love interest, pretty much stayed the same throughout. The story was originally set in a fantasy world instead of a historical setting so the clothes they are wearing in the sketches are not historically accurate.
