Fulk III FitzWarin (c. 1160–1258; alias Fulke, Fouke, FitzWaryn, FitzWarren, Fitz Warine, etc., Latinised to Fulco Filius Warini, "Fulk son of Warin") was a powerful marcher lord seated at Whittington Castle in Shropshire in England on the border with Wales, and also at Alveston in Gloucestershire. He rebelled against King John (1199–1216) from 1200 to 1203, mainly over a dispute concerning his familial right to Whittington Castle, and was declared an outlaw. He was the subject of the famous mediaeval legend or "ancestral romance" entitled Fouke le Fitz Waryn, which relates the story of his life as an outlaw and his struggle to regain his patrimony from the king. He founded, between 1221 and 1226, Alberbury Priory in Shropshire which he granted to the Augustinian canons of Lilleshall but later transferred to the Order of Grandmont. His grandson was Fulk V FitzWarin, 1st Baron FitzWarin (1251–1315).
Fulk III was the son of Fulk II FitzWarin (died 1197) by his wife Hawise le Dinan, a daughter and co-heiress of Josce de Dinan. Fulk II was a marcher lord of Shropshire, the son and heir of Fulk I FitzWarin (d.1170/1) of Whittington and Alveston, who himself was the son of (i.e. in Norman French Fitz, in modern French fils de) the family's earliest known ancestor, thus deemed the family patriarch, "Warin of Meer", from Lorraine.
Warin of Meer the patriarch is however a "shadowy or mythical figure", about whom little is certain. The later mediaeval romance Fouke le Fitz Waryn gives his name as "Warin de Meer". Whatever his true place of origin it is however generally believed that the head of the Warin family came to England during the reign of William the Conqueror (1066–1087). Neither the father nor his sons were during that reign tenants-in-chief, that is to say important vassals or feudal barons, rather their grants of lands were obtained from later kings.