Pérotin was a French composer active in the late 12th to early 13th century who was known as "Pérotin the Great". He was a member of the Notre Dame school of polyphony in Paris and is renowned for developing organum, a style of polyphony where additional voices were added above and below a chant to create harmonies of perfect fourths and fifths. Pérotin began writing organum pieces with three and four voices, advancing the form through techniques like rhythmic modes and voice exchange. His most famous work is the piece "Viderunt omnes" composed in 1198.