How many books does Calvin O'Keefe feature in?

Calvin O'Keefe is a character from Madeleine L'Engle's "Time Quintet," which includes five primary novels: "A Wrinkle in Time," "A Wind in the Door," "A Swiftly Tilting Planet," "Many Waters," and "An Acceptable Time." He plays a significant role in the first three books, particularly in "A Wrinkle in Time," where he is introduced as a key character. His presence is less prominent in "Many Waters" and "An Acceptable Time," where he appears in a more limited capacity.