William Adelin
During king Henry I's lifetime William was invested by Henry as Duke of Normandy. But this was a title he held more in name than practice.  Henry made William the duke when he was pressed by the king of France, Louis VI, to pledge his fealty.  Henry as a king himself thought this was beneath him so in 1115 he offered to have William do this in his place.  The offer was at first refused. But, later after a period of war Louis accepted him. William did homage to Louis VI in the middle of 1120.