Angels
From the Compendium Catechism: 

59. What did God create?

Sacred Scripture says, “In the beginning, God created the heavens and the earth” (Genesis1:1). The Church in her profession of faith proclaims that God is the Creator of everything, visible and invisible, of all spiritual and corporeal beings, that is, of angels and of the visible world and, in a special way, of man.

60. Who are the angels?

The angels are purely spiritual creatures, incorporeal, invisible, immortal, and personal beings endowed with intelligence and will. They ceaselessly contemplate God face-to-face and they glorify him. They serve him and are his messengers in the accomplishment of his saving mission to all.

61. In what way are angels present in the life of the Church?

The Church joins with the angels in adoring God, invokes their assistance and commemorates some in her liturgy.

“ Beside each believer stands an angel as a protector and shepherd leading him to life.” (Saint Basil the Great)

74. What was the fall of the angels?

This expression indicates that Satan and the other demons, about which Sacred Scripture and the Tradition of the Church speak, were angels, created good by God. They were, however, transformed into evil because with a free and irrevocable choice they rejected God and his Kingdom, thus giving rise to the existence of hell. They try to associate human beings with their revolt against God. However, God has wrought in Christ a sure victory over the Evil One.