Looking for word to describe a person amazing because he's so strong and deceitful, but awful for the exploitation and murder. I thought there was an actual word or phrase to describe someone like this?
Super villain ? Maybe not the tone you were looking for, maybe you wanted an adjective, but it's what sprung to my mind.
DonaldTrumpian Hitlerish Stalin impressionist Line cutter (i guess it'd be a 'que' cutter on the other side of the pond) Boy Band supporter politician bureaucrat
It can be tough, as most of the applicable words come off as melodramatic. Diabolical has connotations of complex machinations, like Moriarty. Fiendish, if he takes a malevolent glee in doing bad things. Malevolent, of course, though that actually sounds sort of detached, almost emotionless in his evil. Abominable is a good word, though you always mentally add the word "snowman" at the end. For nouns, you could call him a monster or even the devil.
Vaderesque Demonic Devilish Wicked Depraved Perverse Nefarious Malignant Pernicious Amoral Just a few out of the old Thesaurus. (They are the only dinosaur to not go extinct, and are a writers best friend.)
I find simply describing their negative characteristics is the most grounded, fair way to do it. So liar, thief, murderer, you know, be specific. But if you want a general term from someone who is good at being bad, well, I'm fond of the TvTropes term "magnificent bastard." http://tvtropes.org/pmwiki/pmwiki.php/Main/MagnificentBastard.
When I think of amazingly evil, only my wife's name Kiem Price comes to mind. Rub her the wrong way and she truly fits this description. Twisted comes to mind also, but you pretty much have to add F__k to it to get the point across.