Superman's Evil Persona was a separate being that was created from Superman, due to exposure to Synthetic Kryptonite which temporarily separated him into two beings. Apparently, most of his unpleasant characteristics were imbued on his evil twin, who acted without morals or care for others (Superman III).
As Evil Superman, his suit took on significantly darker color scheme. His overall appearance also deteriorated due to not taking care of himself, as seen by his scruffy appearance and unkempt hair.
When Gus Gorman created synthetic "Kryptonite" on the behalf of Ross Webster, Superman reacted unexpectedly. Gorman, posing as a US Army general, presented Superman with a "jewel" for an earlier heroic act, which was the fake Kryptonite, and was disappointed to see it had no immediate effect. Over time, Superman focused more on destructive acts as opposed to working for the well-being of the people. The evil Superman's acts ranged from juvenille to serious. Some of his more sophmoric acts included blowing out the Olympic Torch or straightening the Leaning Tower of Pisa, whereas he more destructive acts were ripping apart an oil tanker. Evil Superman was also prone to heavy drinking, wallowing in self-pity, and a weakness for women. Lorelei Ambrosia became his mistress, and she got him to do her bidding (actually her boss Ross Webster's wants). Lana Lang wanted no part of Superman, but her young son Ricky, whom Superman had saved prior to his descent into darkness, believed in him and said his bad behavior was merely a reaction to a downturn in life. Although an innocent comment, Ricky's remark caused conflict within evil Superman, in which his soul split into twins, and his remaining "good" part came in the form of Clark Kent. Evil Superman shouted at his hatred of Clark and sought to kill him once and for all, but Clark withstood all attacks and ultimately defeated Evil Superman. His soul once again united, Good Superman was restored.
In Smallville, Jor-El turned Clark into Kal-El. While he is not technically evil, Clark as Kal-El showed no regard for humanity and cared very little about other people. Martha Kent used a chunk of Black Kryptonite to bring back regular Clark. Is notable for having a fully developed ability to fly, something Clark could not conciously do for several years afterwards.