Cte Othon-Guillaume DE MÂCON
- Born: Between 960 and 962, Dijon, Cote D'or, Bourgogne, France
- Married (1): Between 981 and 982
- Married (2): Bef 1016
- Died: 21 Sep 1026, Mâcon, Saone-et-Loire, Bourgogne, France
- Buried: Abbaye de Saint-Bénigne, Dijon, Cote D'or, Bourgogne, France
Also called Guglielmo DI IVREA.
Rodulfus Glaber names "Willemus, Henrici ducis priuignus, Adalberti Longobardorum ducis filius" and records that, as a boy, he was secretly stolen from the land of the Lombards and restored to his mother "with no small cunning by a certain monk". "Einricus…imperator" confirmed the property of the abbey of Fruttuaria, referring to property donated by "Otto qui et Vuillielmus comes filius Adalberti nepos Berengarii regis", by charter dated 1014. It is assumed therefore that Guillaume was imprisoned as a child by Emperor Otto I in Italy after his father and paternal grandfather were deposed as kings of Italy. The Chronicle of Saint-Bénigne, interpolated into the Chronicle of Alberic de Trois-Fontaines, names "Guilelmum Ottonem et eius matrem Gerbergam" when recording that he was adopted by his mother's second husband "dux Burgundie Henricus".
He adopted the name OTHON-GUILLAUME. He succeeded in  as Comte de Mâcon, by right of his first wife. He was declared heir to the duchy of Burgundy and installed as Comte de Nevers by his stepfather in 986. He was recognised as duke of Burgundy on the death of his stepfather in 1002, but deprived of his inheritance by Robert II King of France in Spring 1003 when the latter invaded Burgundy with troops lent by Richard II Duke of Normandy. Rodulfus Glaber records that "Willemus, Henrici ducis priuignus, Adalberti Longobardorum ducis filius" rebelled against the king [Robert II] on one occasion, supported by his son-in-law Landry Comte de Nevers. "Comes Otto" donated property to Saint-Bénigne-de-Dijon for the souls of "Heinrici ducis qui eum loco filii adoptavit et genetricis sue Gerberge uxoris predicti ducis ac filii sui Widonis et Hermintrudis coniugis" by charter dated 1004. Comte Othon continued to claim the duchy of Burgundy, but reconciled himself with the king of France in 1005, finally renouncing his claims in 1015. He was designated comes Burgundiæ, presumably a descriptive title with no precise territorial significance at that time although Othon did own extensive territories in Burgundy.
The Chronicle of St Bénigne de Dijon records the death in 1027 of "Otto qui et Willelmus dictus est comes" and his burial at St Bénigne. The memorial on the tomb of "Nobiliter natus Guillelmus et Otho vocatus" records his death "1027 XI Kal Oct". The necrology of Autun Saint-Martin records the death “XVI Id Dec” of “Guillelmus dux Burgundie, anno 1025”. 1
Othon-Guillaume married Ermentrude DE ROUCY, daughter of Ragenold DE ROUCY, Comte de Reims, and Alberade VON LOTHRINGEN, between 981 and 982. (Ermentrude DE ROUCY was born between 947 and 952 in Reims, Champagne-Ardenne, France and died on 5 Oct 1002/4.
Othon-Guillaume also married Adelais before 1016. (Adelais died on 29 May 1026.)