William of Gellone was a Frankish nobleman and soldier of the late eighth and early ninth centuries who, after a career of warfare and rule in the service of Charlemagne, withdrew from public life to become a monk at the monastery he had founded in the valley of Gellone in southern Gaul. He is commemorated on May 28, the day of his death, and is venerated as a pre-schism Western saint. His monastery, near Lodeve in Languedoc, later took his name and is known as Saint-Guilhem-le-Desert.
Born around the year 755, William belonged to the ruling families of the Frankish realm. His father was Thierry (Theoderic), Count of Autun, and his mother Aldana is traditionally said to have descended from Charles Martel, which made William a kinsman of Charlemagne. He spent his youth at the imperial court and was entrusted by Charlemagne with high office and military command, serving as Count of Toulouse from about 790 and holding the title of Duke of Aquitaine.
As a commander on the southern frontier, William led the Frankish defense against Muslim forces advancing from Spain. The sources record his resistance to an invasion of Languedoc in 793 and his role in the campaign that captured Barcelona in 801. According to the anchor tradition, he forsook arms and rank in later life; having founded the monastery of Gellone in 804 and placed it under the direction of Benedict of Aniane, he himself entered it as a monk in 806 and remained there in humility until his death.
By tradition Charlemagne bestowed upon the abbey a relic of the True Cross. William died at Gellone on May 28, traditionally dated to 812, and his veneration spread widely; his formal canonization in the Western Church is dated to 1066. In the Orthodox tradition he is honored among the saints of the undivided Church as an example of a Christian ruler and warrior who exchanged worldly power for monastic repentance and humility.