In my very first pre-outline ideas about Senta and the Steel Dragon, Iolanthe Dechantagne was going to be the primary character. Senta originally was nothing but a person who would be the eyes through which we saw Iolanthe. As the outline firmed up, it became obvious that Iolanthe would be too bitchy to be around all the time. I got so tired of her that I rewrote her part in book 2 and made Yuah the main character in that book instead.
I don't know where the idea came from for Iolanthe. In a lot of ways, she's a much bitchier version of my mother, at least as I remember her from when I was a kid. Iolanthe has to be really tough to make it in a man's world-- especially a Victorian one. And her history explains a lot about her disposition. Her most distinctive physical feature-- her aquamarine eyes, just came out of nowhere. I was looking for things to make my setting a little more other-worldly and that just popped into being. Her first name came from a baby name web site, but I made up the last name. I wanted something that could have gone from French into English aristocracy.
Because she is such a major BITCH, Iolanthe is a lot of fun to write. She can be very sympathetic and just when you think you're going to start liking her, she does something excrutiatingly mean. Still, she is one of the heroes of the story. So what if she drives her family to distruction, basically enslaves an entire native population, and (arguably) commits several murders.