Guy Fawkes (1570 - 1606) and military conspirator English Catholic; Robert Catesby (1572 - 1605) British politician and author of the "Conspiracy of the powder" concocted against the Protestant King James I. Detail from print depicting the seven conspirators; in a version Colorized. The attack; had it not been foiled because of an anonymous letter; he would massacre the sovereign with all the House of Lords; during the inauguration ceremony of the British Parliament on Nov. 5; 1605.