Births on October 21

Henri de Boulainvilliers, French nobleman (d. 1722)

Henri de Boulainvilliers (French: [də bulɛ̃vilje]; 21 October 1658, Saint-Saire, Normandy – 23 January 1722, Paris) was a French nobleman, writer and historian. He was educated at the College of Juilly; he served in the army until 1697.Primarily remembered as an early modern historian of the French State, Boulainvilliers also published an early French translation of Spinoza's Ethics and wrote on topics as diverse as astrology, physics, philosophy and theology.

The Comte de Boulainvilliers traced his lineage to the House of Croÿ, to Jean de Croÿ, sire de Clery et de Boulainviller, who died in the Battle of Poitiers (1356). At the time of his birth, however, the family's fortune had declined significantly. Much of Boulainvilliers' historical work and political life centered on the decline of the nobility.