Eudes was the Count of Penthièvre, Duke and Regent of Brittany. He was the youngest son of Duke Geoffrey I of Brittany and Hawise of Normandy, daughter of Richard I of Normandy. Odo married Agnes of Cornouaille, sister of Hoel II of Brittany.

Eudes children with Agnes were:
Adele ;
Geoffrey I, Duke of Penthièvre ;
Brian , participated in the conquest of England and received the honour of Richmond, died without issue;
Alain le Roux , which held the honour of Richmond from 1070 to 1093, died without issue;
William d. after 1055/1057;
Robert d. after 1055/1057;
Richard d. after 1056/1057;
Alain le Noir , which held the honour of Richmond shortly after the death of his brother 1093, without posterity.
Stephen , comte de Guingamp de Trégor and Goëlo seigneur, then count of Penthièvre, and which holds the honour of Richmond from 1093.
Eudes illegitimate children,
a daughter married to Enisan of Pleven
Bodin monk at the Abbey Notre-Dame of York
Ravensworth Bardulf
Ribald of middleham married Béatrice Taillebois
Arnold
Brian Earl of Cornwall
At least two of Eudes sons participated in the Norman conquest of England.
His descendants became the junior branch of the Breton ducal family, which eventually gained control of the duchy in 1156 under Conan IV of Brittany.
He was also known as Odo of Rennes