Rocksteady is a villain in the 2012 Teenage Mutant Ninja series. He is introduced as Ivan Steranko in the episode Enemy Of My Enemy. He is a Russian arms dealer with ties to the Shredder and the Foot Clan.
As Ivan Steranko
Steranko wears a black suit with shoulder pads with spikes on it, a black dress shirt, a red tie, an Ushanka with a yellow star on it, and two golden knuckle dusters on his fists, with a hammer on one and a sickle on the other. He is blonde-haired and has a diamond eye, as well as several scars on his face.
He is a mutant human-rhinoceros hybrid, with grey, thick skin and a large horn. His knuckle dusters seemed to have fused with his skin, and now wears army pants and a yellow shirt, with the same spiked shoulder guards he used to wear.
Appears to be close to the Shredder, given an offhanded mention that they're "old friends." He is first seen talking to the Shredder about a weapons deal. He is presumably knocked unconscious by the weapon that was meant to incapacitate the Shredder.
In "The Legend of the Kuro Kabuto", he was revealed to have some past with Anton Zeck, who (allegedly, accidentally), is the one who shot out Steranko's eye. Steranko, an ancient artifacts collector, hires Zeck in to steal the Kuro Kabuto from the Shredder.
Among Steranko's ancient armory are the Spear of Destiny, Excalibur, and the armor of Alexander the Great.
In Serpent Hunt Steranko is stuck in New York with Zeck because of the Kraang invasion. He then decides to capture Karai, Shredder's adopted daughter who has become a mutant snake. After a confrontation with the turtles, the successful duo capture Karai and made a contract with Shredder so that he and Zeck could leave the city. In the end the Turtles release Karai and Steranko and Zeck are captured by Shredder and his henchmen. As punishment, Shredder decides to make mutate Zeck and Steranko. Ivan tries to convince his old friend not to mutate him as he knows himself for ten years. But Shredder the mutated despite all. Zeck is transformed into a warthog and Steranko becomes a Rhino.
In The Pig and The Rhino, which takes place immediately after Serpent Hunt, he and Zeck begin the episode by lamenting the fact they've been turned into "freaks", followed by them attacking Shredder because of the pain and fear of what they've become. Shredder effortlessly defeats the both of them by himself and offers them to either serve him or die, both of them agreeing to serve him. Shredder requests them to find Karai so that Baxter Stockman can attempt to mind control her. On their way, they figure that it's the Turtles' fault that they've mutated, and they should take it out on them. Speaking of the Turtles, they, along with Casey Jones and April O'Neill, are also looking for Karai, who said "comet" before leaving, tasking themselves to search three places. While Zeck finds, attacks and captures Donatello and April, Steranko attacks Casey and Raphael, who, even with their best efforts, can't defeat the super-powered mutant. He is informed by Zeck that the rest of the Turtles are at Coney Island, so they both head there. At the park, Leonardo and Michelangelo have found Karai and managed to calm her down, only for her to be scared off by Zeck and Steranko, who threaten to kill their allies captured in their van. While Leo stealthily picks the lock to the van, Michelangelo distracts the duo by trying to come up with a set of cool names for them, like he usually does in the show. He goes over a couple, until he decides Zeck should be named Bebop and Steranko Rocksteady. Rocksteady really likes his new name and uses it to refer to himself, while Bebop hates his. They are defeated by all the Turtles, with help from Casey, April and Karai. When Karai is trying to scavenge food after she ran away to not endanger the Turtles because of her slowly losing her mind from the mutagen, she gets trapped in a cage by Bebop and Rocksteady, showing they did succeed in their original mission.
In the Noxious Avenger, Bebop and Rocksteady battle the turtles while collecting chemicals to create Shredder's brain worms and accidentally drop a canister of mutagen on local sewer worker, Garson Grunge, mutating him in to Muck-Man. Fed up with being bossed around by Shredder and his henchmen, the duo manipulate Garson int thinking the turtles mutated him and use him to carry out their own nefarious deeds, until the truth is revealed and they are defeated.
In Attack of the Mega Shredder, after Leonardo and Michelangelo are captured by the Foot Clan, Bebop and Rocksteady watch them while Shredder and his minions are preparing to "double-mutate" them. Afterwards, the Turtles trick Bebop and Rocksteady into throwing the three Shredder mutants into the vat, planning to combine them with the turtles to create a giant super mutant, but instead create the titular Mega Shredder.
In Annihilation Earth Part 2, after Splinter and April infiltrate Shredder's lair and get him to agree to helping them fight off the Triceratons, Rocksteady join him and his other minions when they decide to team up. Along with everyone excluding the turtles, April and Casey Jones, Bebop and Rocksteady are both killed when Shredder (quite literally) back stabs everyone by killing Splinter, preventing him from stopping the Black Hole Generator. However, they are saved when the six survivors and the alien cyborg, the Fugitoid, time travel and prevent Shredder from killing Splinter and the Black Hole Generator from going off.
In City at War, Bebop and Rocksteady are seen guarding the now sick and dying Shredder at the end of the episode.
In the next episode, Broken Foot, they accompany Tiger Claw and help him protect the Alumon Chemicals factory and the Foot-Bot assembly factory from Karai, Shinigami, Leonardo and the other turtles.
In The Super Shredder, Rocksteady burst in to Stockman's lab when he hears Shredder screaming, only to become horrified when he sees him mutated into his new Super Shredder form. He and Bebop, along with multiple Elite-Foot Bots, appear at the end of the episode and burst through the wall in front of the Undercity, encountering the Turtles, April and Karai.
In Darkest Plight, which takes place directly after the last episode, they are seen fighting the Turtles, April and Karai. After bursting through the wall, they argue about weather they should squish or blast the Turtles and are then easily tricked by Michelangelo, who delays them long enough for Raphael and Donatello to sneak up and defeat them. After climbing out of the chasm in the Undercity, Super Shredder orders them to search the chasm for Splinter, believing that he may still be alive. Bebop and Rocksteady initially argue over who will go first, but they then decide to simply ambush the Turtles after they have found Splinter and Bebop uses his suit to make them invisible. However, one of Casey Jones' hockey pucks ends up hitting the invisible Bebop right in his snout, blowing their cover. The two mutants then engage Raphael and Casey in a fight and end up losing due to their incompetence.
Steranko is a large, muscular Russian man with a thick accent. Rude and humorless, his most distinguishing feature is that he seems to be missing his right eye, having replaced it with a diamond studded prosthetic.
- Michelangelo gave him the name of Rocksteady. The name has much more to Ivan who even made reference to himself as Rocksteady.