Who is the best dark lord?

Now, I may be biased, but I have long contended that dark lords don’t get a fair shake in literature. I mean, they are often portrayed as failures, but if they were historical figures, they would be legends who compare favorably to the likes of Alexander, Julius Caesar, and Napoleon.

So, who is your favorite dark lord from literature and why? The Black Rider? Arawn Death Lord? Sauron or Morgoth? The Warlock King or Torak the Half-Burned? The Night King or the White Witch? Or some other, less well-known dark lord.

Present company excluded, of course.