"Karolus…imperator Augustus" confirms that "Willelmo comite" replaced "patris sui Bernardi comitis" after the latter was killed, by charter dated 16 Aug 886. His birth date is estimated on the assumption that he was a young adult at the time. He is named as brother of "Hava abbatissa" in the latter's charter dated Nov 893. "Acfred dux Aquitanorum" donated property "pro anima…et avunculis meis Wilelmo et Guarino…" to Cluny by charter dated 2 Oct 927.
He succeeded his father in 886 as Marquis of Gothia, Comte d'Auvergne, de Berry, de Mâcon, de Limousin, et de Lyon. The Chronicle of Saint-Maxence names "Ramnulfus comes…Pictavensis" as "consanguineus…Willelmi…comitis Arvernorum", although the precise relationship has not been traced.
Comte de Bourges 892. Comte de Macon, abbé laic de Brioude 893. He was recorded as dux shortly after the accession of Charles III "le Simple" King of the West Franks in 893, and as dux Aquitanorum for the first time in 909, later known as GUILLAUME I "le Pieux" Duke of Aquitaine.
He founded the monastery of Cluny jointly with his wife by charter dated 11 Sep 910. "Princeps et marchio Willelmus" donated property "in patria Arvernica, in comitatu Brivatense…in villa Carisiaceco" to the church of Holy Trinity "pro…animæ patris mei Bernardi et matris meæ Ermengardis…et sororis meæ Adalendis et filorum eius" by charter dated Nov 916, signed by "Ingelbergæ, Wilhelmi, Acfredi, Bosoni…".
The Annales Masciacenses record in 919 the deaths of “Guilelmus famosus dux Aquitanorum...coniunx eius Ingelberga”. 1