Donald Harry Sadler (1908-1987), British astronomer. Sadler started his career in the Nautical Almanac Office (NAO). The NAO was then merged with the Royal Greenwich Observatory, where he was Chief Assistant (1936-1937), working with the Astronomer Royal. Sadler's major role was as Superintendent of His/Her Majesty's Nautical Almanac Office (1937-1970). He was made OBE in 1948 for his wartime services. He was heavily involved with astronomical organisations, both in Britain and internationally. For the International Astronomical Union he served as General Secretary (1958-1964), Vice-President (1965-1968), and President (1968-1970). He was President of the Royal Astronomical Society (1967-1969).