Iolanthe Dechantagne (pronounced Yo-lon-thee Day-shan-tane) is one of my favorite characters in the series. She is a strong woman and can be a real bitch. I hinted, when I wrote the series, that there was something in her past that drove her to be what she was, and in Brechalon, we see in flashback what that was. This is also something that is resolved in Book 5: The Two Dragons. Iolanthe really is the main character in Book 0: Brechalon and Book 1: The Voyage of the Minotaur. She drives the action and events, and in book 1, we see the beginnings of her growth as a person. This continues in Book 2: The Dark and Forbidding Land. She can be ruthless and mean, and at least in Book 0, cares nothing for anyone except her older brother Terrence.
By book 3: The Drache Girl, Iolanthe has kind of moved to the back of the plot. The great moments that define her life are completed by this time. She still remains a fun character though, and even in book 7: The Price of Magic, she continues to be a driver of story events.