Odo I (Eudes I), called “the Insane”, was Count of Vermandois and Valois from 1080 to 1085 and ruler of Saint-Simon from 1085. The last Carolingian male (from its branch Herbertines), he was the only son of Herbert IV, Count of Vermandois and Adele of Valois.
In 1080 Odo inherited Vermandois from his father and Valois from his mother, although disinherited by Herbert IV. Odo was probably mentally ill. In 1085 the council of barons took the power away from Odo and gave it to his sister, Adelaide, Countess of Vermandois, married to Hugh, son of Henry I of France. Odo was given Saint-Simon.