David Lykken was an American psychologist known for his work in the fields of personality and behavior genetics. He was born on April 28, 1928, and passed away on March 15, 2023. Lykken contributed significantly to the understanding of how genetics influence personality traits and behaviors, often emphasizing the role of heredity in shaping individual differences. Lykken is perhaps best known for his research on twin studies, which helped to establish the genetic basis for various psychological traits. He also authored several influential books and articles, including The Antisocial Personalities, which explored the characteristics of antisocial behavior. His work has had a lasting impact on psychology and the study of human behavior.