Pope John XXIII was head of the Catholic Church and sovereign of Vatican City from 28 October 1958 until his death on 3 June 1963. Pope of the Roman Catholic Church from 1958 to 1963. In 1962, he volunteered as a mediator in the Cuban Missile Crisis between the U.S. and USSR, gaining praise from both sides. He also initiated the Second Vatican Council that same year. Wiki link