Read Job 1:6-12. Note that Satan "enters" in among the assembled (loyal) angels AND that Satan and Jehovah have a conversation. Consider: Now, Jehovah is spoken of as truthful, incapable of
lying, honest and loyal. In contrast, Satan is spoken of as having invented lying (being the very first liar in all creation), and blinding people to truth. For these two to have any conversation it would have to be between two sentient beings. It cannot be God addressing evil in general nor can evil reply in the specific crafty way it did without there being a mind behind it.
Next is the contact that Jesus (who is spoken of as never having committed a sin) had with Satan. Recorded both by Matthew and Luke, Satan challenges Jesus to three specific compromises of faith. In each instance, Jesus, loyal to God and not his own selfish desires, correctly handles the situation. Again, if Satan were merely a disembodied concept of evil, this conversation could not have taken place.
There are other proofs regarding this matter, but as I have mentioned recently, I am striving to keep my posts brief. If you want to read more, here is a pretty extensive article.