The first three on this list have been iconic characters, so for the fourth installment I'm sharing someone perhaps less well known, but just as important to me. To begin, let me say that if you haven't read Lloyd Alexander's Chronicles of Prydain, read them now (well, right after you read my books). I first read them when I was maybe nine or ten, and they're certainly aimed at younger readers, but they're as compelling and textured as the Harry Potter series and much better fare than much of what's out there these days. It's sort of junior varsity Tolkien, drawing heavily from Welsh mythology to build a fantastic world of heroes, wizards, and adventure. It is a fairly standard coming-of-age narrative, though there are sections that still bring me to tears today.
The lead protagonist is Taran of Caer Dallben, Assistant Pig-Keeper, but we're not concerned with him today. Today is all about Princess Eilonwy of Llyr, Daughter of Angharad, Daughter of Regat. You may be passing familiar with her from Disney's hatchet job adaptation of The Black Cauldron (she's technically a Disney princess, I guess), but her character in the books is a wonderful example of a strong, independent adolescent woman determined to be more than a passive love interest and yet still capable of compassion, kindness, and femininity, a mix that the modern truckload of "girl power" fantasy struggles to accomplish. Katniss ain't no Eilonwy. This princess is an heir to great magical power that she sacrifices, choosing humanity and friendship over power and nobility. And through it all she retains an unflagging energy, steadfast loyalty, and a tart tongue.
In all fairness, I'm likely biased given that she was the first girl I ever loved, and love her still.