Satan or the devil and the other demons are fallen angels who have freely refused to serve God and his plan. Their choice against God is definitive. They try to associate man in their revolt against God.
MCITL 10th Anniversary: The Catechism and Scriptures together in the Sunday homily
"The integration of elements of the Catechism of the Catholic Church with the readings from the Lectionary offers us an opportunity to demonstrate how the Word of God is able to animate our personal and communal life with Christ and, at the same time, articulate the Church’s faith that has been immeasurably enriched by the living tradition of twenty centuries."-- Archbishop Donald Wuerl, intervention at the Synod of Bishops on the Word of God