Despite his short reign, Pope John XXIII widened the Church's horizons by calling the Second Vatican Council, the first ecumenical council in a century. John didn't live to see the council through, yet he launched the process that modernized the Catholic Church.
The Council produced revolutionary reforms which included the use of local language rather than Latin for Mass, ecumenical efforts toward dialogue with other religions, and a new, more communicative approach to the world.
Aside from Vatican II, John XXIII is best remembered for his last encyclical letter titled "Pacem in Terris," ("Peace on Earth") in which he asked "all men of good will" to work for peace.
Beatified in 2000 in a ceremony led by Pope John Paul II, John XXIII will be made a saint although only one miracle --instead of the two normally required -- has been attributed to him.
This rush to sainthood, which has also involved John Paul II, has been the subject of a harsh debate in the 1.2 billion member Church.