King John will not go down in English history for anything other than the signing of the Magna Carta, as he tended to be overshadowed and ridiculed by his three older brothers.

John's own father, King Henry II referred to him as "Lackland", due to John's lack of estate, and John grew up somewhat paranoid, & unable to trust anyone. Born on Christmas Eve 1166, to Henry II and Queen Eleanor of Aquitaine, John was their forth son and child and therefore, the last of the Angevin Kings. Henry II died on 6 July 1189 after Richard had declared war upon him, causing Henry to flee across England, an old and broken man. 

Ten years later, when King  Richard (The Lionheart) was on his deathbed, He named John as his successor rather than the true heir, Arthur, the son of their deceased elder brother Geoffrey. John's coronation was held in Westminster Abbey on 27th May 1199. The estate held by this family at that time spread from Scotland, and through France (Gaul) to the Pyrenees. 

The Barons were those who had financially supported John through raised taxes, to fund his efforts at retaining his land in France, which He had completely lost by 1204. John raised taxes without asking, and this was not acceptable according to the "Feudal Law".