Black King

Black King is a kaiju that appeared in Return of Ultraman. He appeared in Episodes 37-38. He is Nackle Seijin's monster. He was originally supposed to be Red King's elder brother, but that idea was scrapped.

Return of Ultraman
After Seagoras and Bemstar were defeated, Alien Nackle sent out his own monster Black King, whom acted as his bodyguard to distract MAT. MAT's weapons were no match for Black King's impenetrable skin, and after a while of fighting Black King soon fled the scene, using a white, gassy smokescreen he exhaled from his mouth. Hours later, Black King is summoned again as bait to trap an emotionally hurting Ultraman Jack, (Alien Nackle (in disguise) killed two of Goh's best friends, including his girlfriend while MAT fought Black King.) However like MAT before him, Ultraman Jack's superpowers were no match for Black King's incredible hide, and the monster beat down Jack. Alien Nackle appeared himself shortly afterwards and both the Monster and the Alien double-teamed Jack until finally Jack collapsed from his injures and was taken to Nackle's planet for execution.

Luckily, Ultraman and Ultraseven arrive and are able to rescue Ultraman Jack from his planned demise. Ultraman Jack thanks his comrades and returns to Earth to face off against both Black King and Alien Nackle once again. At first the battle is in favor of the combined forces of Black King and his Master, but Ultraman Jack manages to fight back, and after tossing him up into the air, Ultraman Jack decapitates Black King.

Mega Monster Battle: Ultra Galaxy Legend The Movie
This Monster reappeared in the movie Mega Monster Battle: Ultra Galaxy Legend The Movie.

Black King is the last monster borrowed by Alien Shaplay (whom in turn, both monster and alien are both controlled by Ultraman Belial) to stop Rei and the Ultra Brothers in their human forms. Rei summons Gomora to do battle and in no time, Black King is killed when Gomora impales him on his horn and then blows him up with a laser.