Who is Buttercup from The Princess Bride and what is their importance?

Buttercup is intended to be the heroine of the story, although the reader may wonder if she is actually heroic. Buttercup is born to a pair of poor farmers living in the Florin countryside. She is a tomboyish child who never bothers to wash herself. Buttercup's favorite activities are riding her horse and tormenting the family's farm boy. Buttercup asks the farm boy to perform numerous tasks throughout the day ranging from difficult to ridiculous. Each time the farm boy answers, "As you wish." Buttercup is nearly sixteen when she finally realizes that she loves the farm boy and that his simple answer is his way of telling her that he loves her too.