Which character(s) has the most impact on the narrator in the begging of the novel?

I might consider Sam. Sam is a beautiful brown-haired, green-eyed girl who wins Charlie's affection from the first days of their friendship. She is the step-sister of Patrick and a close friend of Charlie's, and her conversations with Charlie both reveal information about Charlie's background and help Charlie to process and reflect upon his concerns. Sam assists Charlie in becoming more comfortable in his own skin, bringing him into her group of misfit and outcast friends, as well as encouraging him to participate more in society; for instance, Charlie fills in for a missing actor in the Rocky Horror Picture Show at Sam's urging. Despite Charlie's fervent love for Sam, she is not interested in him at first: she believes she is too old for him, and she is also dating Craig, a young man who is beyond high school age. Yet Charlie has important insights on Sam and Craig's relationship, which falls apart when Craig is discovered cheating: "We accept the love we think we deserve." Throughout Charlie's contact with Sam, the young woman enables him to grow and reflect in positive ways.