Walter de Giffard, 1st Lord of Long Crendon, 3rd Count of Longueville (1010-1085) was the son of Osbern de Bolebec, 2nd Count of Longueville, Lord of Bolebec (970-1023) and Aveline de Crépon (974-1024). He married Agnes Ermentrude Fleitel (1014-1103) and had four children by that marriage.
He was a cousin of His Grace, William the Conqueror, Duke of Normandy (1028-1087) and one of his stout supporters in the Duchy of Normandy. Walter was at the Battle of Mortemer and was among the Norman barons who surprised and defeated Counts Odo and Renaud leading the French contingent attacking Normandy from the east. The Normans attacked the French while they slept, most being either killed or taken prisoner. King Henry I soon thereafter withdrew his remaining forces and left Normandy. In 1054 Walter was in charge of maintaining the siege of Arques castle, against William of Talou, who had rebelled against Duke William.
Walter also fought in Spain against the the Saracens. His epithet le Barbastre was earned when he took part in the Siege of Barbastro, an undertaking sanctioned by Pope Alexander II against the Moors in 1064, one of the more famous exploits of that time. By the time of the Conquest, Walter had returned to Normandy bearing a gift of the King of Spain for Duke William, a magnificent war-horse. The same Spanish war-horse duke William called for on the morning of the Battle of Hastings.
In the preparation stage for the Battle of Hastings, Walter de Giffard was one of the Norman magnates who provided 30 ships for Duke William's invasion fleet. As a reward for his participation, Walter was granted the Barony of Long Crendon which held 107 Manorial Lordships, 48 of which were in Buckinghamshire.
Agnes Ermentrude Fleitel