I think the Devil probably had an agenda, to corrupt the human soul with temptation and knowledge. Though to be the "Devil's advocate" literally, you could say that God was holding down Adam and Eve, and that the Devil was trying to liberate them from their chains of censure.

Fundamentally though the Bible is just a collection of anecdotes and parables, whether there's truly any substance I don't know. Hopefully I'll find out before I die, that would give me some interesting things to think about.

Your question seems heavily influenced by a specific religious perspective. Not all religions consider the "devil" to be "evil" or "bad". For example, even the christian bible says God is all powerful...does it make sense to think satan/devil does NOT do God's will? Even in the scriptures, Satan is always shown to be obedient to what God says to do or not to do. He is also just a creation - a part of all creation - and obeying the will of God. Throughout scripture the Satan/Devil is meant to tempt humans...he is an adversary that is there to challenge humanity. Psychologists are heavily influenced by their own cultural perspective but for a great deal of insight into sata/devil, look to other cultures or religions.

It's a good question to psychologists. I'm studying the devil this week but not if he is real or not, what he would believe, do, or say if he existed. There is no reason not to entertain this, although, that too, could be some kind of falsehood. i knew a doctor once that was a preacher and psychologist at the same time. he only seemed to recognize that things existed like this, so there are bible verses pointing out character traits and ultimately, it is separation from God which is kind of like marriage. it is accepting that a certain party is disjoined or not wanting to engage in holy matrimony with the one true God. this is why so many divorce couples think they are right or even admit they are wrong to deviate or seperate from the real truth. the only reason to ask such questions in my opinion, is to then be more likely to find the one true God and spread his good will. the best indicator is probably not a psychologist, but what you think, so that then, is your answer. The devil probably thinks he knows you better than God does.

So you have to ask yourself, is that true?