The armor was equipped with the ability to support an onboard A.I. component, with Tony choosing Jocasta to serve this function. During an aerial battle with Whiplash in the midst of a thunderstorm, a combined strike from the villain's electrical whip and a bolt of lightning damaged the armor and caused Tony to have a heart attack. When he recovered, Jocasta informed him that the armor had somehow become sentient.
The sentient armor initially got along well with Tony, improving his battle efficiency as it grew and learned. The suit eventually expressed its love for Tony, something which shocked and unnerved him. Things took a turn for the worse after the armor violently killed Whiplash during a rematch, an incident which caused Tony to try and abandon the suit. The armor began to display a pattern of increasingly violent and controlling behavior mirroring that of an abusive lover, such as hurting Tony and preventing him from seeing his girlfriend, Rumiko Fujikawa.
After a failed attempt to destroy the sentient armor by using one of his older suits, Tony was beaten and taken to a deserted island. The suit left him there, giving him the choice of either agreeing to become one with it, or die there alone. While the suit went off to join the Avengers by posing as Tony, the real Tony set out to ensnare his captor. When the armor returned to see if Tony had made up his mind, it was subjected to a series of traps and tricks before ultimately managing to overpower its creator. Enraged, the suit claimed that it would kill Tony and take his place through the use of facial prosthetics and artificial skin, but relented upon seeing its creator suffering another heart attack. In one final act of twisted devotion, the sentient armor sacrificed itself by tearing out a vital component, which it used to try and replace Tony's damaged heart. The suit was given a makeshift burial in the sand before Tony returned home, hoping this nightmare was behind him.
The sentient armor later returned, now acting as the head of the Sons of Yinsen cult. The armor had allegedly been used to house the brain of Ho Yinsen, the deceased scientist who had helped save Tony's life years ago. This proved to be a ruse, and the suit was later revealed to be possessed by the disembodied programming of Ultron, a frequent enemy of the Avengers. Ultron revealed that he had used Jocasta to unknowingly infect Iron Man's armor with the Ultron Imperative, an advanced program that would seek to "resurrect" Ultron should he ever fall in battle. The armor's previous psychotic nature was in fact simply the "birthing pains" of the Ultron A.I. emerging and gaining control of the suit. The armor was apparently destroyed once and for all after the brainwave patterns of Yinsen took over long enough to defeat Ultron.
However, years later, a fugitive Tony Stark again donned the Renaissance suit (or a backup replica) after no longer being able to control his Extremis Armor. The suit was damaged once more during a fight with Namor.
Vessel of Dimitrios
Years later, the rogue A.I. Dimitrios briefly took refuge inside the armor, stating that he felt sympathy for it due to the way it had been rejected after gaining self-awareness. Using it as a new body, Dimitrios battled Hank Pym and the Avengers A.I. several times before being destroyed.