The Interval Between 
The Fourth and Fifth Dooms.
Satan Bound for a Thousand Years.
Revelation 20:1-3.

"And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.

And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,

And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season."

        Satan is called four different names 'Dragon', 'Serpent', 'Devil' and 'Satan'. From these and the fact that he can be bound shows that he is a person because an influence or a principle of evil cannot be bound.