Metalhead is a robotic character that is created by Donatello and, in later episodes, begins to develop a camaraderie with all four of the Turtles. He first debuted in the season 1 episode of the same name.
In this incarnation, Metalhead was originally created by Donatello, using reverse-engineered Kraang technology from an exoskeleton he brought back to the lair in an attempt to "upgrade" his own arsenal (which only consists of a bo staff, which Donnie didn't enjoy using at the time, as it was getting easily blown up in their fights with The Kraang). Donnie could control Metalhead via a NES-like controller, while observing the situation through apparent cameras located inside of Metalhead's eyes. While Metalhead clearly proved to be nearly unstoppable in his brief little fight against Raph, Leo, and Mikey, he was also shown to be far too clunky at times (as demonstrated when the team was running on top of a building and Metalhead was taking extremely loud footsteps) - and thus, he was forced by Leo to sit out a mission to infiltrate yet another Kraang warehouse in an attempt to halt their plan of poisoning the city's water supply with Mutagen. When his brothers became overwhelmed, Donnie was forced to send Metalhead in as a means of assistance. He easily defeated all of The Kraang droids attacking them, but, when his blaster accidentally struck some explosives in the area, this sent Metalhead flying backwards and this knocked the antenna off of his head (this also broke the signal that allowed Donnie to control his own creation). One Kraang, however, realized that Metalhead was made out of their own technology, and it climbed out of it's robot body, opting to gain control of Metalhead by simply climbing right on top of the robot's head. With the signal completely lost, Donnie could not possibly defend Metalhead from The Kraang's control. The now under the Kraang's control Metalhead attacked the Turtles, nearly killing them, until Donnie actually showed up in person, having realized the error of his ways and that a wooden staff can prove to be just as deadly as advanced alien technology...Donnie managed to defeat Metalhead by causing a support pillar to fall on him. The Kraang controlling it then ran off...
In "The Pulverizer", Metalhead makes another - this time brief - cameo appearance in Donnie's workshop. He looks as if he has been fully repaired, but he is inactive for the time being. Metalhead also appears in "TCRI", in which Donnie uses some of The Kraang tech inside of Metalhead to hack into and decode some of the information in one of the aliens' stolen data drives to learn more about their plans...
Metalhead returns to action in "Booyaka-Showdown, Part 1", aiding the Turtles in their prodigious battle against The Kraang; He is apparently now programmed with some degree of independence. Operating without any sign of a direct controller, Metalhead promptly drove The Shellraiser directly into the TCRI building lobby and subsequently attacked all of The Kraang guards there, while the Turtles used their newly-created gliders to infiltrate the building from the roof.
In "Booyaka-Showdown, Part 2", he (while being controlled by Donnie) is seen dancing with the gang during their joyous celebration.
He returns in Squirrelanoids appears out of nowhere and promptly decapitates the robot...when the turtles are too fearful to leave the lair, after witnessing the horrifying mutations of a few problematic mutant squirrels that find their way into the lair and then escape not long after. Thus, Donatello sends Metalhead out into the sewers while controlling him, and both he and his brothers watch as one of The
He makes yet another appearance in, in which he is seen in Donnie's lab helping out by carrying stuff.
His supposed final appearance is in the episode "Metalhead Rewired", when it is shown that Donnie has even further upgraded his artificial intelligence (including the capacity to listen to commands) and he also programmed him with numerous fighting styles, and the ability to simulate almost all fighting styles it encounters (very similarly to the Foot-Bot Soldiers). When the Turtles soon find Spider Bytez being chased down by The Kraang for an unknown reason and then being shoved into one of their vans, they bring Metalhead along to investigate, as he could be a source of assistance...When the van ends up completely disappearing inside a parking garage, Donnie orders his creation to scan the surrounding area for any type of hidden passageway or anything of that sort. When they end up finding an obscure computer, Metalhead is commanded to hack into it in order to make it accessible to them, but the robot is shocked by an electrical surge. Back in the lair, Donnie quickly fixes up Metalhead, but the latter ends up locking the Turtles inside Donnie's lab and he then goes to free the multiple mutants that The Kraang have been abducting in order for them to carry out their own bidding. The Turtles are soon released from the lab by Splinter, are able to pinpoint Metalhead's location, and follow him through yet another passageway that is accessible through a port-a-potty!! They land in an unknown Kraang facility and find Metalhead attempting to free the now mind-controlled mutants. When the passageway above is once again opened, Metalhead sacrifices himself to save the Turtles and all the other mutants. The Turtles quickly make their escape and Metalhead's head actually comes up with them. When asked by Leonardo if he'll rebuild the robotic turtle, Donnie wistfully states he might one day.
- Unlike many other characters that overheard negative comments made by other turtles or were seeking revenge for one reason or another (such as Slash and Chong), Metalhead is the only one to remain loyal to the turtles (as in not turn against them by his own will), actually helping them free mutants from the Kraang, even sacrificing himself, most likely in an attempt to gain acceptance.
- Despite apparently having a voice-box, as shown when a Kraang controls him in his debut episode, Metalhead never actually speaks of his own volition. He communicates exclusively through gestures and generic "robot noises".