The "last days" began with Christ's resurrection, when Satan was formally deposed as ruler of earth. God made His kingdom available at that time.
Satan is the opponent of God, of believers, and of all that is right and good. He may appear as 'an angel of light', but this is only a façade.
Satan was first named Helel, or 'son of the dawn.' When Jerome translated the Hebrew into Latin, he named him Lucifer, or light-bringer, a title of Christ!