Guillem de Machaut was a prominent French composer and poet of the 14th century, known for his significant contributions to medieval music and literature. He is often regarded as one of the first composers to create a unified musical work, blending poetry and music seamlessly. His most famous piece, the Mass of Our Lady, is one of the earliest complete settings of the Mass Ordinary. Machaut's work reflects the complexities of the Ars Nova style, which introduced new rhythmic and melodic innovations. He wrote both secular and sacred music, as well as numerous poems, showcasing his versatility and influence in the medieval cultural landscape.