The Opponents of King John
For the cogent reasons explained here by Anthony Beadles, the revolt against King John was led largely by the Northern barons.
The rebellion against King John that produced Magna Carta is as well-known an event as any in medieval English history, commemorated both in this country and in the United States by memorials and exhibitions. People flock to Runnymede to catch some aura of the event. Yet you will not find there any record of the men who really created Magna Carta - I do not mean the mediators like Marshal and Langton, but those who forced John into accepting the terms: the opponents of the King. They remain remarkably anonymous.
Yet this was a great rebellion: it involved a large part of the English baronage; it captured the capital of the kingdom; it invited the French Dauphin to claim the throne; it went on past John’s death until it ended in the streets of Lincoln in 1217; and it produced the great medieval document - Magna Carta. Yet it has no heroic leader to become a legend, not even a Robert of Gloucester or a Strongbow, certainly not a Simon de Montfort or a Richard of York. There is no one whose statue could be put up outside Westminster Hall.