Is it me, or are all of Marvel's villains just evil to the extreme? Sheesh.Well, to start off with, the guy's a Nazi. He's not one of those types that was just following orders either. He personal led units that were dedicated to nothing but wiping towns of innocent people right off the map.
He tends to look back on the Nazi atrocities as "good times".
In fact, Red Skull kidnapped and killed many high ranking Nazis so he could raise higher i the chain of command. Even Hitler feared being replaced by the guy.
Also, he made his own backup plan in case the Nazis lost the war. It was to build a group of machine that would destroy the entire world.
He gave the orders that led to Bucky's "death". He personally killed a hero that was standing in as the "new" Captain America.
He also once tried to put Hitler's Brain in Captain America's body.
At one point, he also took over Latveria in Doom's absence.
When time started catching up to him and he began aging at an advanced rate, he kidnapped most of Cap's friends and allies an forced Cap to undergo a procedure that would turn him into an old man as well.
He had the government later remove Steve Rogers from the Captain America title and gave it to John Walker (U.S. Agent.)
He became a drug lord selling things even Kingpin didn't want to touch.
He also gained reality warping powers for a time and turned Washington into a hell on earth.