Korak is an extraterrestrial character in the 1987 TMNT cartoon. He's the leader of the Glaxxon Federation and appears in the Cyber Turtles episode.[1]
Korak's ship was carrying an ancient and powerful object known as the Firestar, and upon learning of this, Krang shot it down to Earth. He subsequently captured the Ninja Turtles, and rejected their initial offer of friendship. He imprisoned them on the downed ship, while he and his crew left to find the Firestar. Like the rest of his crew, Korak used a cyber-suit which transformed him into a building-sized cyborg.
Korak soon found himself fighting with Raphael and Donatello again after they took spare cyber-suits from the Glaxxon ship. He had a distinct advantage due to the Turtles' inability to use their weapons, and their general inexperience at using the cyber-suits. However, when Donatello figured out how to use the weapons, the Glaxxons' cyber-suits were destroyed and they were left helpless.
Korak fully expected to be killed by the Turtles, and was shocked when they showed his crew mercy. He agreed to destroy the Firestar, and later bid them farewell as they set out on the journey to do so.