The Ultimate Iron Man's Secret Was Too Terrible For The MCU To Adapt
The Marvel Cinematic Universe wears its Ultimate Marvel influence on its sleeve, but their most important character Iron Man has very little to do with his Ultimate counterpart - by design. Written by famous science fiction writer Orson Scott Card, the series was not as well-received as the other hero revamps in the Ultimate line and was quietly buried and eventually forgotten. Of note is Tony's unique physiology - he's barely even human - and he lives with a secret that was simply too strange for the MCU to adapt.
The MCU owes quite a lot to the Ultimate Universe in terms of visual design. Captain America from the 2011 film Captain America: The First Avenger has a battle-ready suit during his days in World War II with plenty of straps, pouches for equipment and ammunition, and a helmet in place of a cloth cowl he wore in the Silver Age of comics. Hawkeye's more simplistic suit is a far cry from his circus-inspired attire in the prime universe as well. But Iron Man lacks his Ultimate-inspired outfit almost completely (the silver accents and alien-esque helmet are absent), and Ultimate Iron Man is to blame.
In Ultimate Iron Man, tech billionaire Howard Stark creates a spray-on blue bio-armor that prevents most injuries, but eats away at the wearer's skin over time. Meanwhile, Stark's lover Maria Cerrera is working on a virus that regrows limbs and tissue - but Cerrera is accidentally infected with the virus along with her unborn child. Cerrera dies in childbirth, and the infant Tony has been infected with the virus; his skin is hyper-sensitive to the air and he feels tremendous pain. Howard sprays him with the blue body armor, and Tony ceases crying.
It's later determined that Tony's skin is sensitive because neural tissue has grown throughout his body. Tony Stark is effectively a walking brain; Card uses this development to explain Tony's genius intellect. At four years old, he already reads and writes better than most college students, and uses his genius to help his father evade Zebediah Stane, who in this continuity has bought Stark Industries and desperately wants the secret to Howard's body armor. Tony eventually develops a skin-tone variant of the armor, but it has the same weaknesses: while he's no longer blue, the armor washes off easily with soap and water (this means Tony Stark can never take a bath - that is until he discovers alcohol dulls his constant pain).
Despite the science-fiction armor of the titular character 2008's Iron Man is a simple story of a man looking to change and atone for his past sins as a devil-may-care arms dealer. Card's changes to the storyline were perhaps too drastic for both fans and new audience members. Moreover, it follows the modern writer's trend to over-explain items that needed no elaboration, such as the reason behind Tony's genius or his reasons for creating armor (here an extension of his father's bio-armor invention). Some stories work best when diluted down to their core elements, and Ultimate Iron Man was too complex to convey a simple message: that of a person trying to change their profession from a "merchant of death" to an Avenger.