Rocksteady 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.
AppearanceAs 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.
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.
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.