The Dragon: He unknowingly played this for the previous Overlord inhabiting the Wizard's body, offing the other fallen heroes so he could reclaim his throne.

Deity of Human Origin: At the end of Raising Hell the Overlord kills the Forgotten God and becomes the new ruler of the Abyss, which presumably makes him a god.

Darth Vader Clone: Not a completely straight example since his personality and actions are up to the player but his backstory as a Fallen Hero and Magic Knight who was Reforged into a Dragon while always wearing intimidating armour brings to mind this trope.

If you pursue the corruption path, his armor eventually darkens and demonic spikes start growing out of his skin, until the armor is black as night as the spikes on his shoulders reach to the top of his head.

Black Knight: By default, he's an intimidating Tin Tyrant in ridged armor and a spiky helmet.

However, the Minions healed him and branded him their new master depending on the player's actions, he can either be a more benevolent, pragmatic ruler or an out and out tyrant is far worse than his predecessor.

Big Bad Slippage: He started out as another hero who gave his life defeating the previous Overlord.

If you want to be true evil, a lot of innocent people need to die to the Overlord directly. One of the biggest chunks of corruption - and likely to be the last one you need before 100% corruption, is to kill a thousand citizens.

Ax-Crazy: You have to play this way if you want to go for 100% corruption, as the most Evil choice at various points in the game usually involve people getting violently killed, sometimes by the Overlord's hand.

After sufficient upgrades however he can be quite powerful. Authority Equals Asskicking: Subverted in the very beginning where the Overlord can't really stand up in a straight-up fight and relies on his minions.

Anti-Hero / Anti-Villain: A low corruption Overlord is a merciless force towards threats, and seems to very much enjoy the power and position he holds, but he never raises a violent hand towards innocents, and at several points makes choices that are decidedly heroic.An Axe to Grind: His default weapon is a battleaxe.Armed with a suit of heavy plate armor, a massive weapon, and an army of minions he now seeks revenge against the heroes who slew the previous overlord. Awakened by the minions to rebuild and reinstate a reign of terror after his predecessor was slain by heroes.

Overlord vs overlord raising hell