10. Queen Margaery Tyrell, as seen in the novels A Clash of Kings, A Storm of Swords, A Feast For Crows, and A Dance With Dragons by George RR Martin and the show Game of Thrones, portrayed by Natalie Dormer
Unlike so many of the amazing women characters in the ASOIAF universe, Margaery is one of the few we never get a POV chapter for; in fact, everything we know about Margaery, we see through the eyes of other characters, specifically Catelyn, Sansa, and Cersei. And through those observations (and suspicions which have been elaborated on within the show), we get to see that Margaery is far more ahead of the curve than anyone else.
House Tyrell is the very definition of social climbers; they were upjumped stewards who only received Highgarden because they bent the knee to the Targaryens. And, as a result, the rest of Westeros side-eyes them because they're "new money." All Mace Tyrell (Margaery's father) wants is an absolute place in the Westerosi hierarchy, and marrying his pretty daughter to a king is surely the way. First Renly (killed by the shadow baby), then Joffrey (killed by Margaery's grandmother because she knew he would treat Margaery the way he treated Sansa), and now Tommen; thrice wedded and (allegedly) never bedded.
It is not until she weds Tommen that we start to get the best view of Margaery, which is through Cersei's (admittedly skewed) view. Margaery knows she is ultimately a position of incredible power; Tommen is sweet and easily pliable, and, by always arguing against what Cersei says and giving Tommen the things he wants, she begins to exude a great deal of sway over Tommen. The first true show of Margaery's power is when she calls Cersei out for her slip during Tommen's practice at jousting, insinuating very clearly that Robert is not Tommen's father. When Margaery is arrested by the Faith and Cersei comes to see her, we see the true Margaery for the first time; unlike Sansa, Margaery doesn't bother wearing her courtesies like a shield and, instead, tells Cersei exactly what she thinks about her. So far, Margaery has gotten the last laugh; Cersei was shaved, stripped and marched through King's Landing while Margaery was simply released to be held in the Red Keep until trial.
Margaery may not win the game of thrones, but I'd bet money she's definitely going to survive it.
And that's pretty kick-ass.