Iron Man's Godkiller armor was so powerful, not even Tony Stark could control it. After being told the hero was the answer to controlling the massive, Celestial armor, Tony quickly discovered The Godkiller wasn't designed for him to pilot - leading to it getting sent to another dimension. But, before that happened, Iron Man had to act on the fly and hack into the ancient cosmic armor to ensure he didn't get teleported with it.
Tony Stark is no stranger to creating and wearing some impressively powerful suits of armor. Among his best creations include an Iron Man armor specifically designed to take down Thor, another one designed to stop the Hulk, a suit of armor with seemingly no upper-limit in a VR world, and most recently, a living armor that's part symbiote. However, possibly the strongest suit of armor he's ever come across is one he didn't create, as it was believed he was destined to pilot The Godkiller armor, a huge Celestial.
In 2013's Iron Man arc by Kieron Gillen, Carlo Pagulayan, Dale Eaglesham, Scott Hanna, Greg Land, Jay Leisten, Guru-eFX and Joe Caramagna, Tony Stark learned his parents prevented his certain death as a child in exchange for allowing him to be genetically altered by an alien robot named 451. The alteration meant Stark would be able to pilot the ancient Godkiller armor. 451 tried to make good on the deal years later, but when Stark tried to control The Godkiller, it rejected him - leading the robot to send the Celestial to destroy Earth.
Given the sheer power of Celestials - as the god-like cosmic beings are responsible for dictating key moments in Marvel Comics history, including creating the Eternals - Stark had to convince 451 to avoid Earth. But, in doing so, 451 sent the armor towards a fold outside of reality. Thankfully, Stark used the robot's body to hack into The Godkiller armor and escaped right before it was sucked into a black hole.
While destiny might have suggested Tony was supposed to one day gain control of the powerful armor, ultimately, the hero wasn't fit to control the massive Celestial being. It turned out, his brother Arno was the one genetically altered by 451 and supposed to be The Godkiller armor's pilot. In the end, Stark's quick thinking prevented The Godkiller armor was destroying Earth and his own demise. Iron Man gained control of the Celestial long enough to ensure it wouldn't cause more damage to his universe. There's no telling how much destruction would have happened if Tony Stark hadn't redirected The Godkiller armor at the last minute.
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