central hero of some 24 French epic poems, or chansons de geste (chanson de geste), of the 12th and 13th centuries. The poems form what is sometimes called La Geste de Guillaume d'Orange and together tell of a southern family warring against the Spanish Muslims. Modern research suggests that at least part of the Guillaume legend may have been originally localized in the Spanish marches, where sons and nephews of the historical Wilhelmus, a Frankish nobleman (and cousin of the emperor Charlemagne) upon whom the Guillaume of the epics is based, played a part in political events of the 9th century.

Poems in the cycle include the Couronnement de Louis, the Charroi de Nîmes, the Prise d'Orange, the Chevalerie Vivien, Aliscans, and the Moniage Guillaume. The underlying theme is the devotion of Guillaume and his family—to each other, to their championship of Christendom against the infidel in Spain and the south, and, above all, to their ungrateful and uncooperative king, Louis the Pious.

The poems are anonymous and are mainly preserved in manuscripts—which are at least a century younger than the earliest of the poems—that often show evidence of material additions. The problem of dating the poems was further complicated by the discovery, in 1903, of the Chanson de Guillaume, a 13th-century Anglo-Norman text at first generally supposed to represent the earliest form of the Vivien episode. But the early date given to this chanson has not gone unchallenged. The Guillaume cycle was expanded by later poets.