Henry Norris Russell was an American astronomer born on April 25, 1877, in New Jersey. He is best known for his work in stellar classification and the development of the Hertzsprung-Russell diagram, which illustrates the relationship between a star's brightness and its temperature. This diagram has become a fundamental tool in understanding stellar evolution. Russell's contributions to astronomy extended beyond the Hertzsprung-Russell diagram. He also conducted significant research on the structure and dynamics of star clusters and was involved in the study of variable stars. His work has had a lasting impact on the field of astrophysics, influencing generations of astronomers.