Niels Nielsen may refer to: Niels Nielsen (rower) (born 1939), Danish Olympic rower Niels Nielsen (sailor) (1883–1961), Norwegian Olympic silver medalist in 1920 Niels Kristian Nielsen (1897–1972), Danish gymnast at the 1920 Summer Olympics Niels Turin Nielsen (1887–1964), Danish gymnast at the 1908 and 1920 Summer Olympics Niels Erik Nielsen (1893–1974), Danish gymnast at the 1920 Summer Olympics Niels Nielsen (geographer) (1893–1981), Danish geographer Niels Nielsen (mathematician) (1865–1931), Danish mathematician Niels Nielsen (Australian politician) (1869–1930) Niels Nielsen, caretaker of the Old Man of the Mountain