This intellectual biography reveals Albert Eustace Haydon’s growth from a pre-scientific Christianity to a scientific study of religions in light of evolution and pragmatic philosophy. Replacing G. B. Foster in comparative religion at the University of Chicago in 1919, Haydon became one of the most important figures in the development of humanism as a religious movement in North America, providing leadership in the writing of the first Humanist Manifesto in 1933. Today Haydon’s writings remain a most important interpretation of religions from a humanist perspective. This work will be valuable to classes which deal with philosophical, religious, social, and intellectual thought in North America since Charles Darwin.