Alfred Adler was an Austrian physician and psychologist. He collaborated with Freud in the early steps of psychoanalysis until he renounced the theories of the psychoanalytic movement.

He formulated a comprehensive system for understanding and interpreting human behavior, founding the school of Individual Psychology. "The Development of Character" is the main part of his work "Understanding Humanity" (“Menschenkenntnis”, 1927). There, Adler approaches the character of children (especially the more "difficult" ones) with a human perspective in relation to their social environment.

He thoroughly examines the feeling of inferiority, the relationships between the two sexes, and those among siblings. For Adler, understanding humanity is the key to a better society. "Understanding Humanity" is a fundamental work of modern psychology for the entire contemporary world.