In the book, there where a few characters that you can say were struggling for power. One person I would say before everyone would be Luke. His constant training and all his experience would make him fit the discretion also at the end he turned out to be the true lightning thief. Another would be Kronos, although he isn't mentioned until the end of the book, he was the one manipulating everyone's thought and turning the good bad. He gave Luke the idea to steal the master bolt. So either of the two could be the answer. Hope I helped. :)