Brian Weiss is an American psychiatrist and author known for his work in the field of past-life regression therapy. He gained prominence with his bestselling book, Many Lives, Many Masters, published in 1988, which details his experiences with patients who recalled past lives during therapy sessions. Weiss combines traditional psychotherapy with spiritual concepts, suggesting that understanding past lives can help individuals heal from emotional and psychological issues. His approach has attracted both supporters and critics, contributing to ongoing discussions about the intersection of psychology and spirituality.