Could a case be made that K. Rool might not be the most "evil" villain, per se, but the most irredeemable based on his actions?
Nonstop pollution, torturous treatment of both foes and allies, remorseless punishment and death penalties for insubordinate minions, imperialistic tendencies, waging a war of attrition through starving the Kongs, frequent kidnappings, disregard for life, general hatred and d***ishness, dishonesty and cheating. . .
When we had this discussion in here a while back, the only remotely "positive" quality K. Rool has that anyone came up with was "he looks like he's having fun when he's being evil." That's when you know there's a strong case to be made.
I was originally typing this post to argue Bowser as a contender...but:
-Bowser is nice to most of his minions. But they're still terrified of him if they screw up, including Bowser Jr.
-He never imposes death to his insubordinate minions. The worst that trio in Bowser's Inside Story got...was a punishment.
-He kidnaps Peach out of some love, not out of malicious intent, as far as I know. See: (ugh) Mario Sunshine, Super Paper Mario.
-Bowser gets outright furious if you harm Bowser Jr or the Koopalings. For a quick example of the former, see the final boss in New Super Mario Bros. It's expressed through the sudden difficulty spike.
-It's hypocritically heartwarming, but he enforces that no one kidnaps Peach or defeats Mario(especially the latter, see SM64DS) without his say-so. See: Dark Bowser, Count Bleck, Fawful.
-Go Karting With Bowser. See: Every spinoff.
-Bowser never wants to
destroy the world, just
Rool(I'm lame) it. This is HIS world(if you make the sonic reference I murder you :^) ) to do as he pleases, and Bowser will be a Goomba's uncle before he lets anybody destroy it. See: Dark Bowser, Shroobs, Cackletta.
-He's not above working with villains for shared goals or immediate situations. Antasma doesn't count. See: his last second moment with O'Chunks in Super Paper Mario.
-Most importantly, which defeats the case altogether,
he has saved Mario's life and teamed up with him on more than one occasion willingly to defeat a greater evil. See: Bowser's Inside Story*(unwillingly),
this* cutscene from Super Mario Sluggers. Super Mario RPG, Super Paper Mario, god knows how many others,
The Subspace Emissary even though it's not Mario who convinces him.
*Worth noting in cases like these is that Mario and co. has shown kindness to Bowser. I'll sound like a sissy, but I do feel sad in a happy way for the guy when that happens.
<---CAN YOU NOT FEEL BAD FOR THAT. And probably because of that, he saves Mario's life a bit later. That's gratitude right there.
So yeah, I defeated my own argument lol. No contest.