Allen Klein is recognized as a pioneer in the field of gelotology, the study of humor, and the therapeutic humor movement. His journey into this field began in 1974 following the death of his wife from liver disease. Her enduring sense of humor throughout her illness profoundly impacted Klein, leading him to abandon his career as a theater and television scene designer to pursue studies in human development.

As an author and lecturer, Klein focuses on the stress-relieving advantages of humor and the concept of gallows humor. He has authored eight books dedicated to the therapeutic benefits of humor, happiness, and positivity. His work explores techniques for navigating loss, setbacks, and difficult times through laughter. Klein also held the position of president for The Association for Applied and Therapeutic Humor from 2005 to 2006. In addition to his own books, he has edited several collections of inspirational quotations.

The profound personal experience of his wife's passing in 1974 served as the catalyst for Allen Klein's dedicated work in therapeutic humor. Witnessing her maintain her sense of humor despite a terminal illness, Klein was inspired to shift his professional focus. He transitioned from a career in stage and television design to delve into the study of human development, specifically exploring the power of laughter and its healing potential. This personal tragedy transformed into a mission to understand and promote the benefits of humor as a coping mechanism and a source of resilience.

Allen Klein has established himself as a prominent author and lecturer, specializing in the stress-reducing qualities of humor and the specific application of gallows humor. His extensive body of work includes eight books that explore the therapeutic advantages of humor, happiness, and maintaining a positive outlook. These publications offer practical techniques and insights for individuals facing adversity, loss, and challenging life circumstances, guiding them toward finding solace and strength through laughter. His expertise has also been recognized through his leadership role as president of The Association for Applied and Therapeutic Humor.