Born around 1036, Odo was the son of a minor lord of moderate income, one Herluin of Conteville. His mother was Herleva, a daughter of a Falaise tanner named Fulbert. From this marriage was also born Robert of Mortain, Odo’s brother and another of William the Conqueror’s closest supporters. What is more, Herleva had an illegitimate son, born from an extra-marital union with Robert I, Duke of Normandy. Often called “the Bastard,” that son was William the Conqueror.
Being the half-brother of William the Conqueror was beneficial for Odo, but only later in life. Early on, Odo was brought up in the Court of Normandy, and both his lofty education and prominence were settled very early on. As William rose in prominence, so did his brothers. They were evidently closely connected, and supported each other as they rose in the ranks.