Roger de Mortimer, 3rd Baron Mortimer, 1st Earl of March (25 April 1287 – 29 November 1330), was an English nobleman and powerful Marcher lord who had gained many estates in the Welsh Marches and Ireland following his advantageous marriage to the wealthy heiress Joan de Geneville, 2nd Baroness Geneville. In November 1316, he was appointed Lord Lieutenant of Ireland. He was imprisoned in the Tower of London in 1322 for having led the Marcher lords in a revolt against King Edward II in what became known as the Despenser War. He later escaped to France, where he was joined by Edward's queen consort Isabella, whom he took as his mistress.
After he and Isabella led a successful invasion and rebellion against Edward, who was subsequently deposed, Mortimer allegedly arranged his murder at Berkeley Castle. For three years, Mortimer was de facto ruler of England before being himself overthrown by Edward's eldest son, Edward III. Accused of assuming royal power and other crimes, Mortimer was executed by hanging at Tyburn.Roger Mortimer of Wigmore, 1st Earl of March in Wikipedia