Eudes, Count of Penthièvre

Odo I

Duke of Brittany, with Alan III
Reign	1008–1035
Predecessor	Geoffrey I
Successor	Alan III by himself
Regent	Hawise of Normandy
Count of Penthièvre
Reign	1035–1079
Successor	Geoffrey I
Regent of Brittany
Reign	1040 - 1057

Born	c. 999
Died	c. 1079 Cesson
Burial	Saint-Brieuc
Spouse	Orguen-Agnes of Cornouaille
House	House of Rennes
Father	Geoffrey I
Mother	Hawise of Normandy
Religion	Roman Catholicism

Odo of Rennes (Medieval Breton: Eudon Pentevr, Modern Breton: Eozen Penteur, Latin: Eudo, French: Eudes/Éon de Penthièvre) (999–1079), Count of Penthièvre, was the youngest of the three sons of Duke Geoffrey I of Brittany and Hawise of Normandy, daughter of Richard I of Normandy. Eozen married Agnes of Cornouaille (Orguen Kernev), the daughter of Alan Canhiart, Count of Cornouaille and sister of Hoel II, Duke of Brittany who was married in 1066 to Eozen's niece Hawise, Duchess of Brittany.

When Eozen's father Duke Geoffrey I died on 20 November 1008, both Eozen and his older brother Alan were minors.

Duke Geoffrey had initiated a dynastic double marriage with Richard II, Duke of Normandy by marrying Hawise of Normandy, one of Richard's sisters, in 996; this was followed by the marriage of Geoffrey's sister Judith of Brittany to Richard around the year 1000. Alan and Eozen were thus double-first cousins of Duke Richard II's children, including Richard III, Duke of Normandy and Robert I, Duke of Normandy (William the Conqueror's father), nephews of Emma of Normandy, and first cousins of Emma's children Edward the Confessor, Harthacnut, Goda of England, Gunhilda of Denmark and Alfred Aetheling.