Ranulf Flambard (c. 1060 – 5 September 1128) was a medieval Norman Bishop of Durham and an influential government official of King William Rufus of England. Ranulf was the son of a priest of Bayeux, Normandy, and his nickname Flambard means incendiary or torch-bearer, and may have referred to his personality. He started his career under King William I of England, probably in the compilation of the Domesday Book of 1086, as well as being the keeper of the king's seal. On the death of William I, Ranulf chose to serve the new king of England, William Rufus.
Under Rufus, Ranulf continued to hold the king's seal, and also became involved in the financial administration of the kingdom, where he quickly made a name for himself by his novel methods of raising revenue. He was given custody of a number of vacant ecclesiastical offices, administering at one point sixteen vacant bishoprics or abbeys. His many duties have led to him being considered the first Chief Justiciar of England. During Rufus's reign, Ranulf supervised the construction of the first stone bridge in London and oversaw the construction of the king's hall at Westminster. In 1099 he was rewarded with the bishopric of Durham.