Adam and Eve were the first human persons created, but the devil and other angelic persons were created before them. Angels are pure spirits (CCC 328-30). Neither the creation account in Genesis 1 or Genesis 2 discusses the creation of the devil, who is presented in the form of a serpent (see Genesis 3:1). His creation is assumed as well as his fall as he plots against Adam and Eve.
Scripture speaks of the devil and other angels as sinning against God, which resulted in their consignment to hell (see 2 Peter 2:4, CCC 391-93). In Satan’s rebellion, a third of the angels—represented by stars—went with him (see Revelation 12:3-4, 7-12). Stars occasionally represent angels in Scripture (e.g., Revelation 1:20, Judges 5:20). The Latin words—Non serviam—“I will not serve”—are traditionally associated with the devil, who pridefully refused to serve God in his kingdom. Despite their damnation, God allows the devil to be active on earth (1 Peter 5:8-9), though he doesn’t leave us to fend for ourselves. Indeed, Jesus promised to be with us until he returns at his Second Coming (see Mt. 28:18-20), and a key way he does so is through the celebration of the sacraments, particularly the Eucharist, which he commanded us to do “in remembrance of him” (see Luke 22:19-20).