Léonin

Léonin also known as leo was the first known significant conposer of the polyphonic oraganum, he was probably French, and he 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. The name “Léoninus”, which is the name of the Latin diminutive or the name “Leo”, theredore it is very likely tgat Léonins givin name was a french name.
About the early life of Léonin is very little to nothing. Léonin’s works may be called the cradle of weastern art music.His organa are arranged for two vocal lines. One is the chant tune, the cantus firmus, laid out either in notes of undefined length or, in some sections, in a sequence of definite note values; the other is a newly composed melodic descant, a rhythmically controlled coloratura of great ingenuity, coordinated with the cantus firmus. Although organa had existed for some time before Léonin, the separation of these two styles, the “pure organum”—with long chant notes—and what was then called “discant,” where both voices have strict rhythm, was his creation. According to Anonymous IV, “Magister Leoninus (Léonin) was the finest composer of organum; he wrote the great book (Magnus Liber) for the gradual and antiphoner for the sacred service.”
One of his songs.
https://youtu.be/6mYfzf5O8QY