An engaging biography that goes behind the myths to reveal the complex life of a transformative figure in modern American Judaism  Rabbi, writer, teacher, and thinker, Mordecai M. Kaplan (1881–1983) was one of the leading Jewish personalities of twentieth-century America. Founder of the Reconstructionist movement, he was a maverick who reshaped religious faith and practice, generating controversy at every turn. Known for his relentless energy and imagination, Kaplan redefined Jewish identity, emphasizing reason over superstition and intellectual discovery over passive inheritance. He introduced new rituals, reevaluated the role of tradition, and advocated for a Judaism that evolved with the times and fostered an inclusive community. Drawn extensively from Kaplan’s private diaries and correspondence with family and close friends, Jenna Weissman Joselit’s intimate portrait of this influential and iconoclastic thinker sheds new light on the meaning of American Judaism, identity, the limits of belonging, and the role of faith in modern society.