When Dr. Victor Falco reported Rockwell missing on the news, Donatello and April investigate his disappearance hoping to find clues about the Kraang. While in his abandoned lab, they encounter Dr. Falco, who claims that Rockwell had been using mutagen to experiment on monkeys. Donatello also takes a flash drive from the lab containing data on Rockwell's research.
The mutant monkey confronts them later. He attacks and defeats Donatello easily, and is about to harm April, but calms down when she talks to him and then runs away. April and the Turtles later search the city for him. Once they capture him, April realizes that the monkey is Dr. Rockwell. They return him to Falco, who promises to take care of him. But later, while studying Rockwell's flash, Donatello learns that Falco has lied to them about Rockwell and used them to get Rockwell back.
The Turtles return to the lab just after Falco injects the psychic neuro-chemical extracted from Rockwell's brain into his own. Falco defeats all the Turtles easily, but Donatello ultimately wins. The Turtles set the mutant Rockwell free, and he goes in the street. Despite hearing him get into a fight with an angry driver almost immediately, the Turtles decide Rockwell will be fine on his own.
Rockwell is next seen in Metalhead Rewired, as one of the detained mutants in the Kraang prison. After he is freed by Metalhead, he breaks the Kraang droid standing next to his cell, then makes for the portal.
His next appearance is in Battle for New York, where he is shown to be the brains behind Slash's new team the Mighty Mutanimals. He is seen at first being at odds with Donatello about which of them is more intelligent, however after acting out his plan to not only open a portal to Dimension X but also use the portal to teleport the imprisoned New York humans back to Earth while at the same time teleporting the Kraang back to Dimension X Donnie told him that plan was "A stroke of genius".
In Clash of the Mutanimals, Rockwell along with the other Mutanimals interrupted an exchange between Tiger Claw and the Fulci Twins. The twins fire at them, causing a fight between Tiger Claw and the Mutanimals. The twins quickly make their getaway with the cash. Tiger Claw easily defeats them all. Both Tiger Claw and the Foot quickly make off with both Rockwell and Slash, leaving both Pigeon Pete and Leatherhead behind. Rockwell and Slash are seen in Baxter Stockman's lab Rockwell and Slash are used in an experiment to test Shredder's mind control serum. Both Rockwell and Slash are not willing at all with being used as experiments and resist. Slash secretly works on cutting one of the straps holding him with shell, so that he can bust out later and escape, but his plans are put on hold when Stockman demonstrates just how he plans to administer the serum. Fusing the formula into some special, mind-control worms, Stockman picks one up and focuses it towards Slash, making the turtle cry out in pain. The eventually "escape" on their own and aided by both the turtles and their fellow Mutanimals. However, as they run, an army of Foot-Bots chases behind them, which the Turtles and the rest of the Mutanimal team quickly take out to aid Rockwell and Slash. Noticing that the two aren't looking so well, Donnie suggests that they take Rockwell and Slash back to the lair pronto. Once Slash and Rockwell are there, there were treated to soup by Splinter. Raph's glad that both Slash and Rockwell are alright, but Mikey suspects that something's off about them. Rockwell confirmed his suspicions by remembering that he and Slash were experimented on by Shredder. Slash explains about the worms, but never got a chance to say anything more before he have a headache. Splinter was about to get some water when Slash suddenly knocks him to the ground hard. Both Leo and Raph blocks Slash's next attack and pushed him away from Splinter. As Raph takes care of Slash, both Leo and Donnie check up on Splinter. But as they're close, both of them got lifted from the ground by Rockwell's Psychic powers. After Rockwell defeated both Pete and Leatherhead him and Slash he and Slash kidnapped Raphael and take him back to Shredder's lair. When they take him to Baxter's lab where Raphael is given a brain worm. After the worm is placed the turtles and the two Mutanimals not brainwashed arrive to retrieve their friends. After Raphael awakens under Shredders control Rockwell and Slash proceeded to attack their friends. During the battle Rockwell is freed after Donatello realized the method to free him from mind control was to insult him like his brother Leo did to Raph. Once freed Rockwell gives Donatello a backhanded compliment and used his psychic powers to Slash from mind control. Once everyone is freed from being mind controlled Rockwell and the others are soon over powered by the Shredder. Knowing they can't take Rockwell escaped with the others after the turtles used a smoke bomb. Back at the lair, Slash and Rockwell stand before Splinter, Slash offering him some tea and apologize for their actions. Splinter said there is nothing to forgive and that it's Shredder's doing, not theirs. Rockwell thank the others for saving them.
In Dinosaur Seen in Sewers!, Rockwell and Slash are seen investigating the sewers to find the traces of the Kraang. During their search he mentions that Kurtzman had investigated the sewers after sightings of dinosaurmen have been reported lurking through them. Rockwell had at first scoffed this until they ran into one of these dinosaur-men. After encountering Zog Rockwell and Rockwell proceed to defend themselves against him. While trying to fight the Triceraton Rockwell attempts to use his psychic powers only to find he can't manipulate the creatures mind. Using the last of his strength Rockwell uses his psychic powers to astral project his thoughts to the turtles and warned them of the Triceraton. Rockwell and Slash are later found injured by the turtles and are brought back to the lair. While their Slash informs them creature that he and Rockwell encountered.
In Annihilation Earth!, Part 1, after recovering Rockwell and the Mutanimals assisted the turtles and the turtles other allies Mondo Gecko , and Muckman in stopping the Triceraton's plan to invade and destroy the earth using the Heart of Darkness to create a black hole. During the fight Rockwell uses his psychic powers and sensed more Triceratons arriving and ended up defeated and captured in an energy bubble. Though his ally Slash managed to delay black hole generator damaging the timer. In the end he and the rest of turtles allies are captured leading to the Turtles to retreat.
In Annihilation Earth!, Part 2, Rockwell and the other Mutanimals remained captured until Splinter failed to stop the Black Hole Generator due to the Shredder killing Splinter. As the black hole sucked all life into it with Earth, Rockwell is last seen reaching out his finger to Leatherhead.
As of the events of Earth's Last Stand, Rockwell was spared the same fate thanks to the Fugitoid's sacrifice in destroying both the Black Hole Generator and the Triceraton mothership.
In Mutant Gangland, Rockwell and the other Mutanimals, minus Pigeon Pete, as he was replaced by Mondo Gecko, pursue the Fulci Twins of Don Vizioso's Italian Mafia, with Rockwell managing to subdue them long enough to scan their minds and discover the Don's plan to eliminate mutants like himself from NYC. Before Rockwell can go further, The Hammer arrives to incapacitate the Mutanimals and secure the Fulci Twins' escape. Going to warn the Turtles, once they explain the situation with the Don's men, while Donnie and Mondo go to find Raph, Rockwell goes with Slash, Leatherhead, Leo, and Mikey to confront Don Vizioso personally, only to learn while they are there that Donnie and Mondo have been captured by the Mafiosi and Raph beaten senseless. After the Hammer enrages Leatherhead, a fight breaks out, resulting in the Don, Hammer, and the Fulci Twins escaping. Returning to the Mutanimals' base, Rockwell and the others plan an attack on an old hotel where the Don has set up a second base of operations, only to soon have a battered Raph stagger in and apologize for allowing Donnie and Mondo to be captured.
During the attack on the hotel, Rockwell, Slash, and Leatherhead attack the Mafiosi guards, before dealing with The Hammer in a powered suit, acting as a distraction to allow the Turtles to enter and save Donnie and Mondo. After Raph goes to help them after they are overpowered, Rockwell coordinates a team attack with himself, Leatherhead, and Slash, allowing them to catch The Hammer by surprise and defeat him, while the other Turtles and Mondo deal with the Fulci Twins and Vizioso and defeat them as well.
Back in the Turtles' lair, Rockwell and the Mutanimals spend some quality time with the Turtles, watching as Leatherhead and Mondo jump for the same pizza and catch it simultaneously.
Later on, in "Requiem", with Shredder's old lair no longer safe for them, Karai and Shinigami find shelter and safety with Rockwell and the other Mutanimals at their hideout in the Bronx. However, the hideout is soon besieged by the Super Shredder, and despite Rockwell and the other Mutanimals putting up a valiant defense, they are no match for Super Shredder, and their hideout is set on fire. Luckily, they are able to escape, but Rockwell is unable to join the Turtles and their other allies as they split up to look for Super Shredder, leaving it up to Slash and Leatherhead to hunt him down.
However, Rockwell joins his fellow Mutanimals in paying their last respects to Splinter at his grave on April's family's farm in "Owari" after learning of his death at the hands of Super Shredder.
Powers and Abilities
Rockwell's mutated form is incredibly strong, fast, and agile. In addition to his monkey-like abilities, Rockwell possesses a psychic ability to read emotions and sense a person's intentions. This gives him a distinct advantage in evasion and combat. Thus far, Rockwell is the first mutant we have seen lose his ability to speak, resorting to monkey grunts and howls. He is also never seen in his human form.
Prior to Battle for New York, Part 1, Dr. Rockwell was experimented upon by the Kraang, increasing his psychic abilities to the point where he could read others minds, control others minds, and levitate objects through telekinesis. The Kraang's experiments also enabled Rockwell to regain his power of speech and vast intellect. Granted without his psychic-amplifying helmet his powers weren't as powerful, but even so they are a force to be reckoned with.
- When he is still relatively feral, Dr. Rockwell's eyes extend longer when he is angry, and get shorter when he is calm.
- The Monkey Goblins in Mazes & Mutants are based on Rockwell.
- He is similar to DC comics' Gorilla Grodd, both are highly intelligent primates with psychic powers and wear an Amplifier Helmet.
- Rockwell was named "Monkey Brains" by Mikey only in the IDW New Animated Adventures comics, he says he thought he had named him already (during the episode). His action figure and video game incarnation also have this nickname, however.
- Rockwell speaks in faux Received Pronunciation.
- Tom Kenny and Ciro Nieli have collaborated before on Nieli's Super Robot Monkey Team Hyper Force Go! where Kenny played Gibson, the team's scientist and another overly articulate scientifically inclined primate character. Kenny uses an identical version of his voice for the character when voicing Rockwell.
- In the episode Annihilation Earth!, Part 2 when all life is being sucked into the black hole Rockwell and Leatherhead are seen mimicking the pose between God and Adam as seen in the painting "The Creation of Adam", the most famous fresco painted by Michelangelo di Lodovico Buonarroti Simoni on the ceiling of the Sistine Chapel.