Himself. We are given a most interesting teaching on this being in Ezekiel 28 where Satan is shown to with such great details it should leave no question of how and why he did so. Hope this helps.
Satan and the devil are the same being. This is what we have failed to learn Satan is a trinity counterfeiting and opposing the Holy Trinity. We are told that Satan stands in heaven bringing charges against the righteous this is Satan the father. Satan the son and Satan the unholy spirit are now being held in the abyss. Waiting in that jail until he is released from those unbreakable chains and his cell.Why is this important? Because if Satan can be in more than one place at a time he would have to be omnipresent.
The devil. God's word tells us that Satan was perfect until iniquity was found in his heart. He put it there. He thought to himself to set himself in the place of God. He chose to rebel against God's authority, and that rebellion was his iniquity. And yes, Satan and 'the devil' are the same being.