thumb|300px|Robert (Rotbert), Count of Mortain (right) sits at the left hand of his half-brother [[William the Conqueror|William, Duke of Normandy. Robert's full brother Odo (Odo Ep[iscopu]s, "Bishop Odo") sits to William's right, implying his seniority. This scene in the Bayeux Tapestry occurs near Hastings, immediately before William ordered the building of a castle there, shortly before the Battle of Hastings.]]
Robert, Count of Mortain, 1st Earl of Cornwall of 2nd creation (–) was a Norman nobleman and the half-brother (on their mother's side) of King William the Conqueror. He was one of the very few proven companions of William the Conqueror at the Battle of Hastings in 1066, and as recorded in the Domesday Book of 1086 was one of the greatest landholders in his half-brother's new Kingdom of England.
Life
Robert was the son of Herluin de Conteville and Herleva of Falaise and brother of Odo of Bayeux. Robert was born in Normandy, a half-brother of William the Conqueror. and was probably not more than a year or so younger than his brother Odo, born . About 1035, Herluin, as Vicomte of Conteville, along with his wife Herleva and Robert, founded Grestain Abbey in Normandy.
Count of Mortain
Around 1049 his brother Duke William made him Count of Mortain, in place of William Werlenc, who had been banished by Duke William; according to Orderic Vitalis, on a single word. William Werlenc was a grandson of Duke Richard I and therefore a cousin once removed to William, Duke of Normandy.
Conquest of England
In early 1066, Robert was present at both the first Council of Lillebonne, that of William's inner circle, and the second larger council held to discuss the Duke's planned conquest of England. Robert agreed to provide 120 ships to the invasion fleet, which was more than any other of William's magnates. Robert was one of those few known to have been at the Battle of Hastings in 1066. He is pictured at a dinner at Pevensey on the Bayeux Tapestry, seated with his brothers William and Odo on the day of the landing in England.
Lands granted by William the Conqueror
Robert's contribution to the success of the invasion was clearly regarded as highly significant by the Conqueror, who awarded him a large share of the spoils; in total 797 manors at the time of Domesday. The greatest concentration of his honours lay in Cornwall where he held virtually all of that Earldom and was considered by some the Earl of Cornwall. He administered most of his southwestern holdings from Launceston, Cornwall, and Montacute in Somerset. Along with his brother Odo he participated in a revolt in 1088 against William II but afterwards he was pardoned. and chose to be buried at Grestain Abbey in Normandy, William the Conqueror considered him one of his greatest supporters and trusted him with the important county of Mortain. In still another entry Vital tells of his leaving Robert's service abruptly and after being escorted back to him, Robert begged for Vital's pardon for his actions. Robert secondly married Almodis.