6. Stannis & Melisandre Murdering Renly
You can guess from the title that much of the subject matter of Game of Thrones focuses on the struggle for power: to sit on the Iron Throne. The battle really intensifies when the king from the beginning of the series, Robert Baratheon, dies in the first season. Robert has two brothers: Stannis and Renly Baratheon. Stannis as the elder remaining sibling believes his claim to the throne to be the strongest. Renly, meanwhile, wholeheartedly disagrees; he considers himself the far more suitable ruler of the two and is ready to do battle against Stannis to win the throne. Melisandre, however, has other ideas. The Red Woman, as she is sometimes known, has inveigled herself into Stannis' party to the extent that he seems to trust her implicitly. He trusts her so much, in fact, that he is quite happy to let her perform some dark witchery to enhance his claim to the throne. Specifically, she gives birth to a demon of black smoke that assassinates Renly, in what is an extremely cowardly and underhanded - not to mention Machiavellian - way to eliminate a rival, let alone your own brother.