Commander Krang is an alien character from another dimension who will be appearing in Out of the Shadows where it is the first official live-action appearance of the character.
After Shredder escapes captivity in the beginning of the movie, Krang teleported him to his dimension to tell Shredder about his plans for Earth. In particular, three items were scattered across the Earth that had the capability to make a black hole connecting his dimension to Earth. Krang requested that Shredder gather them so that he would be able to invade Earth and rule the world. He also gave Shredder a purple ooze capable of mutating humans. Once Shredder assembled the items together, however, Krang had no second thoughts about betraying his ally, calling him little more than a toy for him to play with. Krang immediately began assembling the Technodrome, but the Ninja Turtles were able to intervene, fighting Krang's android body in the process, and reverse the Technodrome's components to return to his dimension. Defeated and buried under his android, Krang swore that he would eventually return to destroy the Turtles.
Fred Armisen was originally going to voice the character, but scheduling conflicts made Armisen unavailable.