Tonguez
A suffusion of yellow
Yep, he's essentially Shazam's nemesis (they have very similar costumes). Now, he's sometimes helped the good guys, but I think ever supervillain has worked with the good guys sometimes. Even Joker helped Batman beat evil Superman!
Its a little more complicated though since he started as Khem-Adam the hero of Kahndaq channeling the powers of the Egyptian pantheon. He was noted then as just and decent in the service of the Egyptian pharoah, but his turn came when he returned home to Kahndaq and discovered that his homeland had been razed and his family murdered. That incident turned him to vengeance and a sense of "eye for an eye' justice where he is judge and executioner. He then took over the country as a tyrant and began a campaign of conquest,however he was defeated by a coalition of enemies and locked in a tomb for millenia.
Black Adam believes himself a beacon of justice (an eye for an eye) and to also be the most suitable person to lead all humanity. As such he is convinced that any action he takes is necessary for the greater good.