Nightmare

Nightmare is the main antagonist of Kirby: Right Back at Ya!

In the show, he is the CEO of his own company: Nightmare Enterprises, and utilizes it to spread his super evil influence throughout the universe. He conquers planets with monsters he creates and sells through the company.

He does not appear much in the show itself, only occasionally appearing as a shadowy figure in a handful of episodes, and fully appears in the finale.

While he is an intimidating and bloodthirsty warlord, he could also be described as childish. He toys around with the citizens of Dreamland as he has the ability to send planet destroying threats but opts to send monsters that range from "a mild inconvenience" to "causes property damage," only completely destroying the town during the finale.

He also utilizes a chessboard as a way to play out events. In a scene where something goes awry, he destroys the board in a fit of anger.
Nightmare is also very cocky as he assumes that Kirby would be unable to beat him in his own realm. He was wrong. Get this man some friends for real.