Margaery Tyrell

Granddaughter to Mace Tyrell's formidable mother and a far shrewder political animal than her father, Margaery belongs to the generation that inherits the wreckage of Robert's reign. She married into the Baratheon name after his death, at a point where the name meant considerably less than the Lannister blood standing behind it.

She appears in the lineage as a branch grafted onto a tree that was already, secretly, not what it appeared to be — which is a neat summary of what Robert's marriage did to the royal succession.