Metalhead was created by Donatello, using salvaged a Kraang droid body in an attempt to "upgrade" his weapons. Donnie could control Metalhead via a NES-like controller, while observing the situation through a TV monitor, through cameras in Metalhead's eyes. While Metalhead proved to be nearly unstoppable in combat situations, he was far too clunky and heavy to properly sneak around, thus leaving him forced to sit out a mission against the Kraang. When his brothers became overwhelmed, Donnie sent Metalhead in. He easily defeated the Kraang attacking them, knocking off the control antenna in the process. One Kraang, however, realized that Metalhead was made from their technology, and detached from its robot body, opting to control Metalhead. With the signal lost without the control antenna, Donnie could not defend Metalhead from the Kraang's control. The now Kraang-controlled Metalhead attacked the turtles, nearly killing them, until Donnie showed up in person. Donnie managed to defeat Metalhead by crashing a support pillar on it. The Kraang controlling it ran off.
In "The Pulverizer", Metalhead makes a brief cameo appearance in Donnie's workshop. He looks as if he has been repaired, but he is inactive for the time being. Metalhead also appears in "TCRI", where Donnie uses the robot's Kraang tech to hack into one of the aliens' stolen data drives to learn more about their plans.