W.D. Hamilton, or William Donald Hamilton, was a British evolutionary biologist known for his groundbreaking work in the field of population genetics. Born in 1936, he is best recognized for his theories on kin selection and inclusive fitness, which explain how certain behaviors can evolve based on genetic relationships among individuals. His influential ideas have significantly shaped our understanding of social behaviors in animals. Hamilton's most notable contribution is the concept of Hamilton's rule, which mathematically describes the conditions under which altruistic behaviors can evolve. His work has had a lasting impact on evolutionary theory and has influenced various fields, including sociobiology and behavioral ecology. Hamilton passed away in 2000, but his legacy continues to inspire research in evolutionary biology.