According to William Rubinstein, Professor of History at the University of Wales, Aberystwyth, the richest person in British history was Sir William de Warenne, First Earl of Surrey, who he estimates to have been worth a staggering £57 billion in today's values.

Born close to the River Varenne, near Dieppe, in Normandy, De Warenne followed Duke William of Normandy on his 1066 expedition to England and was at the battle of Hastings. De Warenne was granted land in Sussex on which he built Lewes Castle, eventually extending his holdings to 16 counties, notably Yorkshire and Norfolk.

He married Gundrada of Flanders, who may have been a daughter of his patron, William I. After a stay at the priory of Cluny in Normandy in 1077, the newly-weds were caught in a Channel storm, and William vowed to found a priory himself if they were spared. They were, and he kept his vow, building the great Cluniac Priory of St Pancras in his fiefdom of Lewes. He supported William Rufus for the crown on the death of William I, and was rewarded with the earldom of Surrey and yet more land.

He stayed loyal to Rufus when the king's uncle Bishop Odo, rebelled in 1088, but was mortally wounded besieging the rebel held Pevensey Castle. De Warenne died in Lewes Castle on 24 June 1088 and was buried at Lewes Priory alongside Gundrada, who had died in 1085.

His descendants, the Dukes of Norfolk, still live at Arundel Castle.

Written by Nigel Jones. 
Published in the BBC History Magazine.

Please note that in 2007 a new list was produced, it placed William de Warenne in second place but increased his fortune to £96 Billion.