Well compared to god the devil doesn't kill so much, in the OT god is responsible for over 2 million deaths, while the the devil can hold his hands up to 10. That's pretty outstanding eh?
No. You're not interpreting this right. The devil is responsible for every death. Think back to the garden of Eden. The command of God was, "do not eat of the tree of knowledge of good and evil,
for you will surely die." By tempting Eve to disobey God's command, the devil caused the death of all men, "because all sinned" (Rom 5:12).
The death of men was the prescribed response to sin from the beginning. It is still the command of God. It cannot be changed. The devil works within that framework to effect the spiritual death of all men, and works to this day. As physical death is inevitable, the devil isn't so much interested in it directly, for it is but the corrolary to his work started in Eden. Death is the appointed judgement of and preserve of God.
Now however the power of the devil is limited (due to Christ's victory as seen in the christianization of so much of the world down the ages). So he generally tends to work by seduction to sin in libertarian societies, but in authoritarian societies he can work in the traditional manner by precluding the knowledge of God by imposition of false religion or fascist law.
What is the character of the devil? The espistle of Jude is excellent: v8 "In the very same way,
on the strength of their dreams these ungodly people pollute their own bodies, reject authority and heap abuse on celestial beings."
The devil is a dreamer and a deceiver. Every gnostic doctrine of modern pseudo-science, law, culture, aesthetics etc is from the devil. Love of the world and material possessions is from the devil. Every pseudo religious cult based on superior gnosis is from the devil. Anything that corrupts the reality of human existence is from the devil. The devil asserts that everything in the world is his possession. In reality nothing is his.