Red Skull/YMMV

Chaotic Evil: Type 4, and a good example of intelligent and calculating Chaotic Evil. The Skull has no ethical or moral restraints on his behaviour and regularly plots the collapse of civilization. He is power-hungry, but his motive for gaining power is pretty much so he can use it to oppress, torture and kill people for his own amusement. He enjoys being a Bad Boss and generally acts like a dick even in his day-to-day life, meaning he tends to torture and kill random people on whims for little or no reason other than he enjoys it. At one point he even formally embraced Chaotic Evil as a political philosophy because he though Fascism was "out of date", whereupon his goal was to create a a violent world with no laws or government where the strong would fight and conquer the weak and each other without anyone or anything to hold them back. He also has a bad, bad case of Chronic Backstabbing Disorder and tends to screw over anyone who does not submit to his leadership (and many of those who do), and if you think you are working with the Skull or even if that he is working for you, you won't have to wait long to find You Have Outlived Your Usefulness.
Complete Monster: Probably the worst in the MU (among normal-ish humans, anyway) and that's saying a lot. There literally is nothing he hasn't done or tried to do somewhere down the line.
- Trying to kill his own daughter because she was not a son... Is not good.
- His favourite weapon, Red Dust/The Dust of Death, is not pleasant either.
- Participated in the Holocaust.
- Regularly kills all but his best subordinates in various gruesome ways, typically the aforementioned Dust of Death, sometimes for trifling reasons. The ones he doesn't kill aren't treated much better and are constantly demeaned, and sometimes assaulted, usually if they are women.
- How did Captain America know this was the real Red Skull? He was using a Cosmic Cube to murder thousands of people indiscriminately, laughing maniacally as he did.
- Is the mastermind and financial backer behind numerous far-right terrorist cells and Fascist movements, using them to try and crash the prevailing social order, typically by getting them to commit atrocities and acts of violence.
- In a Bad Future the Skull used the Cube to warp reality and Take Over the World- as the new God-Emperor, he caused all sorts of natural disasters and killed probably millions of people, including floods, famines and storms all targeting major population centres. He then showed up in person at each of these disasters just to let people know he won't be saving them.
- Let's not get started on his treatment of Mother Night, a supervillainess who became his "girlfriend". While Mother Night was far from a saint, she doesn't really deserve to be a victim of one of the worst cases of domestic abuse in the history of comics. The Skull beat her savagely and regularly, and once dated Madame Viper partly just to screw with her. And Mother Night ended up becoming completely psychologically dependant on him and once even begged him to kill her rather than let her "fail him" all the time: he said he wouldn't, because thats what she wants him to do, and was laughing as he said it. Harley Quinn and The Joker have a healthier relationship. And to top it off, this was the woman who raised his daughter for him.
  - On one occasion, she was late for a meeting. In front of the rest of his henchmen, the Skull told her that the next time she was late, he would have a clock face tattooed on her tongue.
Magnificent Bastard: Depending on the Writer. The version who appeared in Spider-Man: The Animated Series definitely belongs on the list.

"Do not despair Chameleon. The Red Skull anticipates everything."

Moral Event Horizon: As a young man he murdered a teenage Jewish girl when she rejected his clumsy and creepy advances, even though otherwise she liked him and was willing to overlook it. He thought it was the best rush of his life and it served as a release for all the pent up anger and frustration he felt towards the world. One of the reasons he joined the Nazis was for more opportunities to have a rush like that, and it still serves as one of his prime motivations for his numerous crimes.