thumb|200px|Parker. Attributed to John de Critz, .
William Parker, 13th Baron Morley, 4th Baron Monteagle (15751 July 1622), was an English peer, best known for his role in the discovery of the Gunpowder Plot. In 1605 Parker was due to attend the opening of Parliament. He was a member of the House of Lords as Lord Monteagle, the title on his mother's side. after King James I took the throne. Monteagle even went as far as writing a letter to his new king with a promise to follow the state religion. Like some reformers, Monteagle blamed his childhood for his previous wrongdoings, stating: "I knew no better." Though more tolerant than others before him, James was still faced with plots and schemes by priests and rebels trying to end the mistreatment of Catholics through force (Fraser 63). To please the Protestants, who were distressed over the growing strength of the Catholic religion, James proclaimed his detestation of Catholics in England. Those present at that first meeting with Catesby were Thomas Wintour, John Wright, Thomas Percy and Guy Fawkes.]]
On 26 October 1605, while sitting at supper at his house in Hoxton, London, he received a letter warning of the Gunpowder Plot. It read as follows:
It is believed by some historians that he wrote the letter himself to win acclaim and favour with the King.
Later life and death
In 1609, Parker invested in the second Virginia Company and became a member of the council. He had shares in the East India and North West Companies as well. Monteagle gave permission for his eldest daughter Frances Parker to become a nun, although not willing, at first, to grant her request. He eventually surrendered to his physically handicapped daughter's appeal "in respect that she was crooked, and therefore not fit for the world."