These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Dork Age: Sometime around the 1990s, the Skull openly denounced Nazism, supposedly because it was getting old-fashioned: In the future, he'd be a much more dynamic villain. In other words, the guy who had previously spent most of his adult life fighting fanatically for Hitler's dream suddenly and for little reason threw it all away, in order to indulge in pure, sadistic For the Evulz villainy. Later characterizations have since reverted to the Nazi Skull, though there's still considerable flip-flopping on whether he's primarily a Nazi Tautological Templar or merely a crazy sadist scumbag who likes Putting on the Reich.
A recent miniseries by Greg Pak heavily rewrites the Skull's original origin story, which was substantially based on the real Hitler's early life, and attempts to establish him more firmly as The Sociopath, among other things showing him as a mass murderer and Knife Nut long before he became the Red Skull. Fan opinion is divided on whether this is a good thing.
Hilarious in Hindsight: The original inspiration for the Skull? Joe Simon saw a hot fudge sundae shaped vaguely like a human torso. He'd originally planned a villain called Hot Fudge until he realized the cherry looked a lot like an exposed skull. So...
Moral Event Horizon: As a young man when he murdered a teenage Jewish girl for rejecting 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.
Unpopular Popular Character: In universe he's quite possibly the most hated character in the Marvel Universe, outside of it, he's widely considered to be among Marvel's greatest villains.
Famously, in a Marvel/DC crossover, the JOKER refused to have anything to do with him.