Reuven (Robert or Bobby) Malter: a Modern Orthodox Jew, and a teenage boy. He is smart, popular in his community, and has a head for mathematics and logic. His father wants him to be a mathematician when he grows up, but he desires to become a rabbi.
Daniel (Danny) Saunders: a Hasidic Jew, who is also a teenager. Brilliant; with a photographic memory, and interested in psychology (particularly Freudian psychoanalysis) but lacking in aptitude for mathematics. He wants to become a psychologist, but he feels trapped by the Hasidic tradition which forces him into the role as next in line to succeed his father as Rabbi and tzaddik. This fact is a prominent personal conflict for Danny throughout the book.
David Malter (Reuven's father): a Talmudic scholar, writer, schoolteacher at his son's yeshiva, motivational speaker on acts of Zionism and a Zionist himself. Considered a heretic by the Hasidim. Supports the creation of the state of Israel because of his belief in the Messianic Age, rather than a literal Messiah.
Rabbi Isaac Saunders (Reb Saunders): Rabbinic sage and tzaddik. He is Danny's father. Rabbi (spiritual leader/teacher) of a Hasidic group, whose role is dynastic (passed on from father to son). He moved his congregation from Russia to the United States before the October Revolution. He is against a secular Jewish nation-state, because he believes this supersedes God's will. He is also against all who identify as Zionists and follow the belief of a Messianic Age and wish for a secular Jewish nation-state.