Margaery Tyrell

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"I don't want to be a queen. I want to be The Queen"

Margaery Tyrell is one of the more smarter and political characters playing the Game of Thrones. Instead of letting herself be used as a pawn and sold off to broker alliances on her father's bidding, she initiates pairings and fully participates in the politics. A beautiful young girl of 14 at the start of the book (she's aged up in the show), she is first married to Renly Baratheon which brings the Reach into the war against Lannister rule. Later after Renly's death she advocates to become betrothed to Joffrey to bring the Tyrell's into King's Landing, who then accepts the request.

As the only daughter of Mace Tyrell, she is seemingly trained by her grandmother to be graceful and cunning. She is a very driven woman who also is kind to Sansa and the common folk (also gaining their trust and love).  As Tyrell men start bringing food and supplies into the starving city in her name, she gains more power in the eyes of the people as the queen they have desperately needed, which she capitalizes on. Her true motives (other than being Queen) are unknown, but she tries to come off to sincere to Cersei, who is troubled by the newcomer. With Sansa, she is friendly and offers advice to her about her marriage to Tyrion and comes off as more of a mentor and ally, which shows that she can be trustworthy.

We have already seen that she is willing to do whatever it takes to get what she feels she understands and deserves. This includes trying to convince the then-living Renly to have a baby despite his relationship with her brother and trying to capitalize on that situation (seemingly with Loras' approval). She is everything that Cersei desires to be and will be a great Queen but that burgeoning conflict will definitely be one to watch. Knowing what she knows about about Joffrey's nature, we will get to see how she can shape that and attempt to gain the upper hand and prevent coming into any harm from him. This will be a great season to watch as we will see her grow as a character just coming into power and we will also see how she will wield it and what, if any conflicts she will get into. I, for one, feel that there is more to her than meets the eye and that should could really change the political landscape in King's Landing for the better.