Alvan Clark (March 8, 1804 – August 19, 1887), born in Ashfield, Massachusetts, was an American astronomer and telescope maker. He was a portrait painter and engraver, but at the age of 40 become involved in telescope making. Using glass blanks made by Chance Brothers of Birmingham and Feil-Mantois of Paris, his firm Alvan Clark & Sons ground lenses for refracting telescopes, including the largest in the world at the time: the 18.5-inch at Dearborn Observatory at the Old University of Chicago (the lens was originally intended for Ole Miss), the 26-inch at the United States Naval Observatory, the 30-inch at Pulkovo Observatory (destroyed in the Siege of Leningrad; only the lens survives), the 36-inch telescope at Lick Observatory (still third-largest) and later the 40-inch at Yerkes Observatory, which remains the largest successful refracting telescope in the world.