Guillaume Dufay (c. 1397-1474) was a pivotal figure in the transition from the medieval to the Renaissance period in music. He was predominantly a composer of sacred music but also contributed to secular genres, making him a key figure in the development of early polyphony. Dufay’s style is characterized by rich harmonies and the use of fauxbourdon, which influenced later composers. Notable works include the "Missa Se la face ay pale," one of the first settings of the Mass to incorporate a secular melody, and various motets like "Nuper rosarum flores," which was composed for the consecration of the Florence Cathedral. His use of cantus firmus and structured forms laid groundwork for the later development of the mass and motet. Dufay's impact on music is significant; he helped establish the Franco-Flemish style, which became dominant in Europe during the late 15th and early 16th centuries. His innovations in musical form, harmony, and texture influenced subsequent composers such as Josquin des Prez and Palestrina, solidifying his legacy as a crucial figure in Western music history.