After gaining the power of the Infinity Stones, Gamora created Warp World, a pocket universe within the Soul Gem in which every soul in the universe was merged with another. Iron Man and Thor were merged together to become Stark Odinson, the prideful son of Asgard's Chieftain Executive Howard Odin. In order to punish his son's hubris, Howard stripped him of his godhood and banished him to Midgard with no memories. The amnesiac Stark only possessed intuitive knowledge of Asgardian technology, and put it to use to become an industrialist under the identity of Sigurd Stark.
Stark became embroiled in the plans of the Dark Elf-King Malekith, whose alliance with Stark's resentful adoptive brother Stane led him to orchestrate an attempt on Sigurd's life. Stark was ambushed and poisoned by a squadron of Dark Elves, but their commander Krimson Kurse ordered them to keep Stark alive and had him work with another prisoner, the weapon-smith dwarf Eitri. Stark and Eitri conspired to forge a suit of armor to grant Stark the power and protection necessary to take down their captors. When finished, the runes on the suit's chest plate also stopped the poison flowing through Stark's veins from reaching his heart and reversed its detrimental effects. When Krimson Kurse approached Eitri's forge, the dwarf decided to sacrifice himself to buy Stark enough time to regain his strength. Before leaving to his death, Eitri unveiled to Stark the final piece of the suit, a hammer forged from cold iron which acted as the key to unlock the full power of the armor. Stark suited up as the Iron Hammer, and defeated his captors before taking the fight to Malekith and liberating Asgard from his assault.
The design of the Iron Hammer Armor consists of a hybrid of Midgardian technology with that of the other Ten Realms, derived from the intuitive knowledge on Asgardian technology that Stark kept when made amnesiac. The runes engraved in the suit's chest-plate acted both as a power source and a method by which the advance of the poison in Stark's body was reversed as well as the detrimental effects caused by it, like Stark's crippled leg. The suit mainly provides enhanced endurance and durability, allowing Iron Hammer to tangle with foes like Krimson Kurse and Malekith and withstand powerful attacks like a concussive blast from the Vanaheim-Ring.
The final piece of the armor which unlocks its full power is Mjolniron, a hammer made of cold iron. The hammer can be used to release powerful electrical discharges and concussive blasts, and also absorb energy. The armor features an operative system named H.E.I.M.D.A.L.L. with an infallible targeting system, which Stark gloated could see for him if he were blinded. The suit itself blurs the lines between science and magic, allowing Stark to create such things like the B.I.F.R.O.S.T., an idea Stark had just conceptualized when H.E.I.M.D.A.L.L. interpreted its creation as a command to execute. The suit's helmet can additionally seal itself and provide its user with a supply of ten minutes of air.