Léonin

Léonin (also Leoninus, Leonius, Leo; fl. 1163–1190) was the first known significant composer of polyphonic organum. He was probably French, probably lived and worked in Paris at the Notre-Dame Cathedral and was the earliest member of the Notre Dame school of polyphony and the ars antiqua style who is known by name, thanks to the writer known as Anonymous IV. Though no further identification is certain, the name "Leoninus" and its Latin diminutive Leo have the French equivalents Léonin/Léo.