Robert's birth-date ranges between 1051 and 1053. As a child he was betrothed to Margaret, the heiress of Maine, but she died before they could be wed, and Robert didn't marry until his late forties. In his youth he was reported to be courageous and skilful in military exercises. He was, however, also prone to laziness and weakness of character that discontented nobles and the King of France exploited to stir discord with his father William. He was unsatisfied with the share of power allotted to him and quarrelled with his father and brothers fiercely. In 1063, his father made him the Count of Maine in view of his engagement to Margaret, and Robert may have had independent rule in Maine. The county remained under Norman control until 1069 when the county revolted and reverted to Hugh V of Maine.
In 1077, Robert instigated his first insurrection against his father as the result of a prank played by his younger brothers William Rufus and Henry, who had dumped a full chamber-pot over his head. Robert was enraged and, urged on by his companions, started a brawl with his brothers that was only interrupted by the intercession of their father. Feeling that his dignity was wounded, Robert was further angered when King William failed to punish his brothers. The next day Robert and his followers attempted to seize the castle of Rouen. The siege failed, but, when King William ordered their arrest, Robert and his companions took refuge with Hugh of Chateauneuf-en-Thymerais. They were forced to flee again when King William attacked their base at Rémalard.
Robert fled to Flanders to the court of his uncle Robert I, Count of Flanders, before plundering the county of the Vexin and causing such mayhem that his father King William allied himself with King Philip I of France to stop his rebellious son. Relations were not helped when King William discovered that his wife, Robert's mother Queen Matilda, was secretly sending her son Robert money. At a battle in January 1079, Robert unhorsed King William in combat and succeeded in wounding him, stopping his attack only when he recognised his father's voice. Humiliated, King William cursed his son. King William then raised the siege and returned to Rouen.
At Easter 1080, father and son were reunited by the efforts of Queen Matilda, and a truce lasted until she died in 1083. Robert seems to have left court soon after the death of his mother, Queen Matilda, and spent several years travelling throughout France, Germany and Flanders. He visited Italy seeking the hand of the great heiress Matilda of Tuscany (b. 1046) but was unsuccessful. During this period as a wandering knight Robert sired several illegitimate children. His illegitimate son, Richard, seems to have spent much of his life at the royal court of his uncle William Rufus. This Richard was killed in a hunting accident in the New Forest in 1099 as was his uncle, King William Rufus, the next year. An illegitimate daughter was later married to Helias of Saint-Saens.