Short answers, pulled from the story.
Simon de Montfort, 6th Earl of Leicester, was a French-born English nobleman who lived from around 1208 to 1265. He led the baronial opposition to King Henry III, briefly became de facto ruler of England, and convened the parliament of 1265 that is regarded as a foundational moment in the history of representative government.
Montfort's Great Parliament of 1265 summoned knights from each county and two elected representatives from a select list of boroughs, including ordinary citizens from English towns. It is regarded as a key step in the development of modern parliamentary democracy because it extended representation beyond the nobility to include townspeople, a precedent that shaped the later House of Commons.
Simon de Montfort was killed at the Battle of Evesham on the 4th of August 1265. Roger Mortimer stabbed him in the neck with a lance. Prince Edward had assembled a twelve-man death squad before the battle with the sole purpose of finding and killing the earl.
Royalist forces mutilated Montfort's body after the battle. His head and testicles were severed and the head was sent to Wigmore Castle as a gift to Maud, wife of Roger Mortimer. The canons of Evesham Abbey buried what remains could be found before the altar of the abbey church.
Simon de Montfort expelled the Jewish community from Leicester in 1231, banning them from the city permanently. During the Second Barons' War, his followers massacred Jews in London, Worcester, Winchester, Derby, and other towns, seizing debt records stored in locked chests called archae. Around 500 Jews were killed in London alone, and Leicester City Council formally rebuked Montfort for his anti-Semitism in 2001.
A relief portrait of Simon de Montfort adorns the wall of the Chamber of the United States House of Representatives, recognising his role in the early development of representative government. He is placed among historical figures associated with the foundations of law and democracy.