allegedly first bishop of Paris, a martyr and a patron saint of France.

According to St. Gregory of Tours's 6th-century Historia Francorum, Denis was one of seven bishops sent to Gaul to convert the people in the reign of the Roman emperor Decius. Little is known of his life; it is believed that he was martyred during the persecution of Christians by the Roman emperor Decius in 251 or Valerian in 258. In the 7th century his relics, which had been founded shortly before by the Merovingian king Dagobert I, were moved to the abbey of St. Denis, near Paris. In the 9th century, Hilduin, abbot of St. Denis, translated the mystical works of Pseudo-Dionysius, which had been sent to the emperor Louis I the Pious by the Byzantine emperor Michael II. The abbot identified the Parisian Denis with Pseudo-Dionysius (Pseudo-Dionysius The Areopagite), who was believed to have been the Athenian disciple of St. Paul the Apostle (Dionysius The Areopagite) but was most likely a Syrian monk of the 5th or 6th century. In the 12th century, Peter Abelard was forced to flee the monastery and France itself when he sought to demonstrate that the Parisian Denis and the Athenian Denis were not the same person.

A legend recorded in the 9th century recounts that Denis was beheaded on Montmartre and that his decapitated corpse carried his head to the area northeast of Paris where the Benedictine abbey of St. Denis was founded. Denis is often portrayed in art as a decapitated (though evidently living) figure.