Catechism of the Catholic Church §2864 — excerpt
In the last petition, "but deliver us from evil," Christians pray to God with the Church to show forth the victory, already won by Christ, over the "ruler of this world," Satan, the angel personally opposed to God and to his plan of salvation.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.