According to Islamic doctrine, even Satan, or Lucifer, Beelzebub, or whatever else he was called, was a Moslem.
According to Islamic doctrine, anyone who is submissive to the will of God, anyone who does what he does according to what God has willed him to do, was a Moslem.
Satan does what he does according to what God has willed for him.
In other words, Satan, by not doing what God has not willed for him, is therefore submissive to the will of God, as were all murderers, rapists, liars and so on, all being submissive to and doing the will of God according to what God has willed for them, not doing what God has not willed for them.
In other words, they were all Moslems, Satan included.
Q.E.D.
