Satan is not imaginary, nor is he a myth, as many--including Satan--would have us believe. Jesus speaks of him as a real being.
The Bible describes Satan as an angelic being, who was once in Heaven. He rebelled against his Creator, God the Father. Satan is a created being, who was once the model of perfection. See Ezekiel 28:12 and Ezekiel 28:15 in the Old Testament. He became prideful. Wickedness was found in him and he was thrown out of heaven.
The name Satan is derived from the Hebrew word meaning "act as an adversary." He is our adversary, trying to keep us from our true home.
The word devil is also used to describe him. It is from the root word meaning accuse. He is known as the accuser. He accuses us of sin. Sometimes-too often-we listen to him, believing that we are not worthy to approach God. But Jesus Christ has paid the price for all we've ever done or will do wrong, so we are pronounced innocent. We confess the sin to the Lord and we are forgiven. With Jesus Christ as our savior, we are sinless before God.
In the book of John - John 8:44 - Jesus describes Satan as a murderer. He says that when Satan lies, it is completely consistent with his character; for he is a liar and the father of lies.
In the book of Revelation - Revelation 9:11- Satan is called Abaddon. He is the personification of death and destruction. In Greek, he is Apollyon.
As described in Luke 4:1-13, at the beginning of His ministry, Jesus went into the desert and fasted for forty days. There, He had a conversation with Satan. Satan tried to tempt Jesus to give up His God-given mission on earth - the mission that would remove us all from Satan's power. Jesus was not deceived by Satan's lies and half-truths. Jesus' allegiance was only to God the Father.
Satan is a fallen angel.
He is our adversary.
He is an accuser.
He is a murderer.
He is a liar and the father or lies.
He is death and destruction.
He is defeated!
"Yes,' he told them, 'I saw Satan falling from heaven as a flash of lightning!
Don't be deceived. Listen only to Jesus. Know what the Bible teaches.