French abbot of the Benedictine monastery of Cluny (1049–1109), under whose direction medieval monasticism reached its apogee and Cluny won recognition as the spiritual centre of Western Christianity. He also helped develop the liturgy of the Latin rite.

Hugh de Semur took monastic vows at the age of 14 and, in 1049, succeeded Odilo (later St. Odilo) as abbot. Under Hugh's rule, nearly 2,000 monasteries associated with Cluny were founded in Italy, England, and Spain; in 1055 he founded the first Cluniac convent, at Marcigny. While encouraging the development of Cluniac monasticism elsewhere, he also expanded the parent house at Cluny; at his death, there were 300 monks.

Hugh had a personal reputation for wisdom, sanctity, and persuasiveness, evident in his diplomatic missions to Hungary and Germany on behalf of the church. Before being elected abbot, he had served as the abbey's ambassador to the Holy Roman emperor Henry III. Later, during the reign of the subsequent emperor, Henry IV, Hugh acted as an adviser to Pope Gregory VII in the investiture controversy, a struggle for power in which the emperor attempted to transcend papal authority.