Lucifer, also known as Satan or the Devil, is a Fallen Angel and main adversary in the Christian faith. He stands in opposite to God, Jesus Christ and humanity as a whole.
While Christianity is a monotheistic religion who believe in one deity, the Trinitian God (Father, Son, Holy Spirit), Lucifer is often referred to as the "god of this age" (Holy Bible, 2 Corinthians 4:4).