This article memorializes Harold Mosak (1921-2018), one of more important interpreters of Adlerian psychology, who died June 1, 2018, at the age of 96. Mosak cofounded the Alfred Adler Institute, now Adler University, in Chicago in 1952. He worked with clients and mentored students until his retirement from clinical practice and the classroom in 2015. He was a prolific writer, authoring nearly 200 articles and books about Adlerian psychology. (PsycINFO Database Record (c) 2019 APA, all rights reserved).