Rollo May (1909-1994) was an American existential psychologist. He was the author of several influential books, such as Love and Will and The Courage to Create. May adopted a humanistic and existentialist perspective, which, along with Viktor Frankl, made him a leading researcher and theorist in the area of human existential crises. He created a theory of various stages during the human lifespan, which differs from other developmental theorists’ stages. May also contributed to the contemporary understanding of human sexuality.