Alvan Clark was an American astronomer and telescope maker, born on March 8, 1804. He is best known for his work in the 19th century, particularly for creating some of the largest and most powerful telescopes of his time. His telescopes were used for significant astronomical discoveries, including observations of the planet Mars and the double star system. Clark co-founded the Alvan Clark & Sons company, which became renowned for its high-quality optical instruments. His legacy includes the Great Refractor at the University of Chicago, one of the largest refracting telescopes ever built. Clark passed away on August 19, 1887, leaving a lasting impact on the field of astronomy.