Walter of Douai (Old Norman: Wautier de Douai) (born c.1046, died: c.1107) was a Norman knight, probably at the Battle of Hastings, and a major landowner in South West England after the Norman Conquest, being feudal baron of Bampton in Devon and of Castle Cary in Somerset. He is given various names and titles in different sources including: Walter (or Walschin or Walscin) de Douai. Douai is sometimes written as Dowai. He has also been called Gautier de Douai and later Walter the Fleming.
Walter was the son of Urso of Douai, that was then a fiefdom of the counts of Flanders and now is a commune in the Nord département in northern France. Located on the river Scarpe some 40 km from Lille and 25 km from Arras. He may have had two brothers Fouque and Goselin, who also fought at the Battle of Hastings and another brother Hugh who did not come to England.
He married Emma (or Eddeva) of Devon, and may have had two children Richilde de Douai and Ralph (of Tintinhull) Lovel. He also had a second wife. His son Robert built Bampton Castle in Devon.
Walter likely fought at the Battle of Hastings in 1066, though he is not among those for whom proof of participation has been found.
In the aftermath of the victory, William the Conqueror entrusted the conquest of the south-west of England to his half-brother Robert of Mortain. Expecting stiff resistance, Robert marched west into Somerset, supported by forces under Walter of Douai, who entered from the north; a third force, under the command of William de Moyon, landed by sea along the Somerset coast.