Robert Trumpler was an American astronomer born on December 2, 1886, in San Francisco, California. He is best known for his work in the field of stellar astronomy, particularly for developing methods to measure the distances to stars. Trumpler's research contributed significantly to our understanding of the structure and composition of the Milky Way galaxy. One of his notable achievements was the discovery of the Trumpler classification system, which categorizes star clusters based on their brightness and concentration. Trumpler also studied the effects of interstellar dust on the light from stars, helping to refine distance measurements in astronomy. He passed away on March 10, 1956.