A:
Perhaps Leo III's greatest failure was in his opposition to changing the Nicene Creed to suit contemporary theological inclinations. Leo forbade the addition of Filioque ("and the Son") to the Nicene Creed, when asked to confirm the decision of a Council of Aachen held in 809. He also ordered that the Nicene Creed, without the Filioque clause, be displayed on silver tablets placed in Saint Peter's Basilica, adding: "Haec Leo posui amore et cautela orthodoxae fidei" (I, Leo, put these here for love and protection of orthodox faith). In spite of this, the Filioque clause eventually became part of Catholic doctrine, although it played a major part in the Great Schism of 1054.
Pope Leo XIII was the pope in 1896. He was pope from 1878 to 1903.
Pope Leo became the Pope in 1513, his name also changed from Giovanni di Lorenzo de' Medici to Pope Leo.
No, Pope S. Leo the Great was not married.
Pope Leo XIII was an excellent pope and a prolific writer of encyclicals.
Pope Leo I died on 461-11-10.
Pope Leo V died in 903.
Pope Leo II was born in 611.
Pope Leo IV was born in 790.
Pope Leo III was born in 750.
No, Pope Leo XII has not been canonized.
Pope Stephen IV was chosen after the death of Pope Leo III.
He chose the name Leo at the time of his election as pope.