Ahsoka Tano from The Clone Wars
Ahsoka Tano is nothing short of a miracle. First appearing in the pilot movie of a television series that wasn't initially well received, introduced as a Padawan apprentice to Anakin despite having never been mentioned in any of the preceding films, and characterized as a brash teenage girl who had difficulty following orders (fandom hates a teenage girl at the best of times, making her butt heads with male authority figures was practically a death sentence), she was poised to become the most loathed Star Wars character since Jar Jar Binks.
Roger Ebert himself had this to say about her: "Ahsoka Tano, by the way, is annoying. She bats her grapefruit-sized eyes at Anakin and offers suggestions that invariably prove her right and her teacher wrong. At least when we first met Yoda, he was offering useful advice."
The deck was well and truly stacked against her, and so what happened next was astounding: she became one of the most popular characters in the entire franchise. In what is perhaps the most breath-taking case of Rescued From the Scrappy Heap since 24's Chloe O'Brian, the show's writers stuck to their guns, course-corrected the ship, and turned Ahsoka into an earnest, loyal, conflicted, brave and ultimately tragic figure.
And make no mistake: The Clone Wars is fundamentally her story. Rey might be the first female protagonist of a Star Wars film, but the distinction of first female protagonist period goes to Ahsoka. She grows from a fourteen to a seventeen year old across the course of the show, and despite its format – a series of mini-arcs that focused on a wide range of characters – its underlying structure was built upon Ahsoka's maturation.
Here is a child-soldier that was thrown into mortal danger, forced to watch people she cared about suffer and die, driven into leadership roles far beyond what would normally be expected of someone her age, and who is eventually betrayed by the very Jedi Order that raised her. Yet for all of this, she does not break; she does not relinquish her moral compass.
In this respect it's fascinating to watch the dynamic between herself and Anakin, not only for its brother/sister/student/mentor rapport, but in the way each one is indelibly shaped by the conflict tearing up the galaxy around them. Each one goes through their own personal crucible set against a backdrop of war and hate and violence, but only she emerges with her soul still intact.
The culmination of her character arc at the conclusion of the fifth season adds a particularly tragic note of irony to her story: leaving the Jedi Order may break her heart, but it also saves her life. More than that, it leaves a series of "what might have been" questions in her wake. Had she not left the Jedi Order, would Anakin have fallen to the Dark Side? Would she have been enough to keep him tethered to the Light? We'll never know, but it serves as a reminder that it's our choices more than our circumstances that define who we are. Anakin broke, but Ahsoka remained true to herself.
(Oh, and did I mention her distinctive fighting style? She has two lightsabres, each one wielded not as a sword but a dagger, the blades pointed inwards and used to shield her body. It's cool).