Coldsteel is a robotic gargoyle, formerly a flesh-and-blood member of the Wyvern Clan before his death in the Wyvern Massacre. His soul was one of three souls that were used to resurrect the cyborg Coldstone, before he was subsequently transferred into a robotic body.
Before attaining his own body, he was referred to in production material and by fans as Iago, although that name was never used in the series itself.
In the Kingdom Hearts Unlimited Saga, Coldsteel is a minor antagonist. First appearing in a cameo role in "The Keyblade Wars", Iago originally served as a spy for the Archmage Destane within the Wyvern Clan before their castle was taken over by the Horned King. After being discovered, Iago was trapped in a stone spell by the Archmage and subsequently left to be shattered during the Massacre for his failure. A thousand years later, Iago's soul would later be reawakened within Coldstone's chassis and then transferred by Emperor Zurg's heart-removal laser beams into an Android body built by Dr. Gero to serve the Dominion XIII as an acolyte. Instead, Coldsteel betrayed the Dominion to try and cause chaos on his own terms. In "Return of the Keyblade", Coldsteel pledged his services to Maleficent in the hopes of using his past relationship with the Archmage to help her in finding the fabled Tome of Prophecy.