Theobald III of England (II of Navarre) (1238 - 4 December 1270) was king of England and Navarre from his father's death in 1253 to his own in 1270. A regent ruled in his place until 1256, when he turned 18, and this turned him against the nobility.
Theobald III was born to the successful Troubadour and crusader Theobald II, who had united Navarre and England by succession. This caused moderately large ramifications in that the King had to spend most of his valuable time travelling between London and Pamplona through the semi-hostile Kingdom of France. The Regent, John of Avesnes, Count of Hainaut and Anjou, who was a descendant of Henry II, felt that this was a massive waste of time and advocated a policy of seizing all the land in between the Bloisevin lands in Northern France (Blois, Chartres, Chateaudun, Champagne, Normandy and Flanders) and cajoled the nobles into declaring war on the Duchy of Aquitaine (ruled by Adelaide of Burgundy at the time). The young King was firmly against such an opportunistic war and was justified in this when the war turned into a costly and overwhelming disaster. This solidified his hatred of the barons of both his realms.
Upon his majority, Theobald called the first Parliament since the 1230s, not only as a source of revenue but to cultivate favour with the bourgeoisie and involve them in government. This earned him the scorn of his fellow rulers. In 1266, he administered the first census of modern times, in order to tax his people more effectively. Theobald married the daughter of the King of France in order to improve foreign relations but all this got him was the responibility of going on Crusade with Louis IX, who was regarded by all and sundry as a romantic nutter. Louis died of dysentry at the Siege of Tunis in North Africa, which was conceived as a way of outflanking the entire Arabic region but when it was realised that the journey fom Tunis to Jerusalem would take something in the region of three years the whole army went home and Theobald died while stopping over at Sicily. He was succeeded by his brother, Henry IV of England.