I seem to go through phases with my novel protagonists. The main characters will have a common underlying type for a series of projects; then that type will change completely. By type, I don't mean that a specific cookie-cutter or exact set of characteristics - just an overarching "feel."
I don't make this decision consciously, either to begin the streak or to end it ... and because I'm frequently in different stages in multiple projects at once, I don't always have a clear sense of the transition.
I recently finished one of these streaks - if you can call a few years ago recently. Has it been that long since I finished Who Wants To Be A Hero? Because that was the end of the previous streak: characters who were quiet, self-contained, independent ... but not necessarily sure of their course in life. It's Rhiane in Journal of the Dead, who endured the weight of ghosts to search for her son; Anaea in Scylla and Charybdis, a fish out of water in her tiny home colony who discovered the true size of the universe; and Ioweyn in Who Wants To Be A Hero? who willingly allowed herself to be a prize in a game to earn herself a divine role. These women are very different, but they share the same heartbeat.
The next streak started with Unnatural Causes, which I'm doing editing notes for now, and this set of protagonists promises to be a lot ... livelier. The dominant thread seems to be a snarky-sarcastic attitude, little patience for authority, and a strong will: not only a descriptor of Vil, who refused to be treated as a creature (she was a mage's familiar) as she tried to solve her mistress' murder; but a good descriptor of Maren, the protagonist of the still-unnamed project I'm working on now. I have a backup concept in the works with a wild-child sorceress who finds herself in possession of a rich mystic legacy in the form of enchanted dolls ... you can see the common thread, I'm sure.
Why do I do this? I'm not sure. Perhaps it's me as a person - less than as a writer - working through something in my life. Maybe I'm channeling some aspect of myself that is important at the time - this would fit with the previous streak, as I was feeling aimless before I decided to enroll in culinary school. Maybe it's wish fulfillment, something I lack - certainly, I can't just shake people off the way my current protagonists can. Is this a writer's version of therapy?
Am I going to break the streak now that I'm aware of it? Probably not. The characters are still different enough to keep me out of a rut (or the accusation that I'm writing the same person all the time, should I be lucky enough to get each book in print). And as a backburner thinker, I've learned that most of the time, it's best to let my subconscious mind have at it.