Simon de Montfort led a rebellion, successful for a time, against King Henry III of England, and paid the ultimate price at the battle of Evesham, falling in defeat to the forces of Edward (at the time, Prince of England).
“Simon de Montfort was born in France in about 1208. His father was a large landowner, but when he died he left his land to Simon’s older brother Amaury. The de Montfort family had owned land in England in the past and Amaury suggested that Montfort should visit Henry III in to see if the land could be reclaimed.
Montfort arrived in England in 1230. Henry liked Simon, was sympathetic to his claim and gave him back his family lands. The king also agreed that Montfort should become the new earl of Leicester. In return, Montfort promised to pay a fee of £100 and to supply sixty knights in time of war.
The new earl of Leicester also agreed to become the king’s steward, which involved him in organizing ceremonial functions. This pleased Montfort as it enabled him to meet most of the rich and influential people in England. As he was short of money Montfort hoped that this would help him to meet a rich widow.” http://www.spartacus.schoolnet.co.uk/NORmontfort.htm
Simon married King Henry’s sister–a scandal at the time since the King opposed the marriage and she was the richest widow in England.
“What instigated the rebellion of 1258? Henry had been king for forty-two years, and had proven himself to be a very poor ruler. He was wholly incompetent, a poor governor, resisted Magna Carta, and repeatedly denied the barons their rightful position as his counselors. The rebellion of the barons against Henry was not instigated by Simon alone. At the beginning of the baronial movement, Simon was merely one of many dissatisfied barons, and could hardly have been regarded as their “leader.” As a result, no strictly contemporary account casts Simon as the sole leader, or even as one of the more prominent leaders in 1258.
“While Simon was one of the sworn signers of the 12 April Confederacy, which began the revolutionary movement, he was also one of the twenty-four authors of the Provisions of Oxford, a member of the fifteen-man privy council, and sat on other committees, as too did the earls of Gloucester, Hereford, and Norfolk, Roger Mortimer, John fitz Geoffrey, Peter de Montfort, and the Bishop of Worcester. . . .
“As 1263 began, the barons grew increasingly dissatisfied with Henry and his “leadership.” As in 1261, a large number of barons organized and approached Simon, asking for his support in a rebellion. He was reluctant to join, but did so at the request of Gilbert de Clare, son of the deceased Richard of Gloucester. The barons’ disgust soon turned to rage, with Louis IX of France’s issuance of the Mise of Amiens. Louis had been cast in the role of arbitrator of the dispute between Henry and Simon over the Provisions of Oxford. As was to be expected, Louis sided with Henry, and “freed him from obedience to the Provisions, which, (he) stated, ran directly against the holy and royal rights of kingship.” The Mise of Amiens proved to be the spark needed to begin the Battle of Lewes. With this battle, Henry’s forces were defeated, he was imprisoned, and his son and heir to the throne, Edward, was taken hostage to ensure Henry’s good behavior. After the battle, Simon became the de facto head of the English government. Simon ruled England in Henry’s name for the next fifteen months.” http://www.triviumpublishing.com/articles/simondemontfort.html
Montfort recognized Llywelyn ap Gruffydd as the Prince of Wales in 1265 and held him enough of a friend to offer Llywelyn his daughter in marriage, but he’d been unlucky in battle, and in the end, the rising star of Prince Edward couldn’t be stopped. Edward, who’d actually joined the barons against his father back in 1259 had switched back before the armed conflict began, and now took advantage of the barons’ weakness and pugnacity. By the end, he convinced all but a very few to come over to his side, whether with cajolery, righteous anger, or outright bribes.
The last battle at Evesham is described in detail here: http://www.simondemontfort.org/battle_of_evesham.htm