Who wrote the first polyphonic setting of the mass?

The first polyphonic setting of the Mass is attributed to the composer Guillaume de Machaut, who lived in the 14th century. His work, "Messe de Nostre Dame," is considered one of the earliest complete settings of the Mass Ordinary in polyphony. Machaut's composition marked a significant development in the history of Western music, showcasing the intricate interplay of multiple vocal lines.