Satan is a real personality, identified at the very beginning of the Bible (Genesis 3:1) and the very end (Revelation 20:10), with many references in between.
Jesus considered him to be a real personality and rebuked him with God's Word (Matthew 4:1-11).
Satan is a created being, he was not eternal with God in the beginning; but he is not human with a natural lifespan. He is a spiritual being without a body, as are the angels, and he can masquerade as an angel of light, to suit his dark purposes.