Petyr Baelish
After learning the abuses Sansa Stark suffered by Joffrey, Olenna figured out that Margaery could avoid the same fate by using Joffrey's love of violence. Varys warns Olenna that Petyr Baelish has designs on Sansa, who, given the death or disappearance of all her brothers, is now the key to the North. Olenna thus secretly plots to have Sansa marry Loras. Her plan is foiled by Loras himself, who accidentally reveals it to his new lover, one of Baelish's spies. Baelish informs Tywin Lannister, who has Sansa marry his son Tyrion Lannister instead. To secure the Reach, Tywin orders his daughter Cersei to marry Loras. Lady Olenna is at first against this because Cersei is too old (and therefore unlikely to have more children) and because of the scandal of her incestuous affair with her twin brother Jaime. But after Tywin threatens to make Loras join the celibate Kingsguard, which would make Joffrey and Margaery's children the heirs of Reach, Olenna admits defeat and praises Tywin for getting the best of her.