From Wikipedia:

Rollo Reese May (April 21, 1909 – October 22, 1994) was an American existential psychologist and author of the influential book Love and Will (1969). He is often associated with humanistic psychologyexistentialist philosophy and, alongside Viktor Frankl, was a major proponent of existential psychotherapy. The philosopher and theologian Paul Tillich was a close friend who had a significant influence on his work.[1][2]

As well as Love and Will, May’s works also include The Meaning of Anxiety (1950, revised 1977) and, titled in honor of Tillich’s The Courage to BeThe Courage to Create (1975).