A monster under the command of the Assassin Alien, Alien Nackle, that planned to assassinate Ultraman Jack. Black King was given training based on Ultraman Jack’s combat data. Therefore, Black King was impervious to Jack’s Spacium Beam or special attacks from his Ultra Bracelet. Black King possesses super strength and can attack with heat rays from his mouth.

Black King appeared from underground to stop MAT as they transported a new model of liquid explosive called Saturn Z. Black King distracted the MAT members so that Alien Nackle could steal Saturn Z unnoticed. Then Alien Nackle killed Ken Sakata and his sister Aki. Hideki Go was consumed with rage and transformed into Jack to fight against Black King when he appeared in Tokyo. Black King nullified all of Jack’s attacks and defeated him with the help of a giant Alien Nackle.

Later when Jack is revived, once again Black King and Alien Nackle team up against Ultraman Jack and overpower him, but in the end Black King is defeated by Jack’s Slice Hand attack.