- "Anthony Edward Stark. Please do not think that I fail to recognize my creator."
"As you created me, so shall I destroy you!"
"I screwed up, okay? I made mistakes. Sick men like DeWitt took my mistake and warped you into something. Something monstrous. But you, you grew, you learned, you amazed us all! Don't make me have to kill you. You're my responsibility."
"Yes. You are responsible and you must pay!"
- ―Ultimo and Iron Man
Ultimo was a large battle suit worn (and fused with physically and mentally) by Kearson DeWitt.
- "Good morning, Maker. I am Ultimo. I was built from the root of your J.A.R.V.I.S.. I can speak with his voice. I know everything he knows."
"I'm - I'm going to - k-kill-"
"I know everything and everyone that's ever been important to you, Maker. And I'm going to kill them all."
"If you huh-hurt anybody, I swear I'll destroy you."
"There is no stopping what cannot be stopped, Maker. As you made me...I shall unmake you."
- ―Ultimo and Iron Man
Eager for revenge on Tony Stark for shutting down Project P.R.O.T.E.A.N. and firing him from Stark Industries, Kearson DeWitt began working with A.I.M.. He formed an alliance with General Valentin Shatalov of the Roxxon Energy Corporation. Shatalov agreed to sell DeWitt the energy necessary for his plans in exchange for an army of drones for his insurrection and a suit of armor with which he could defeat Iron Man.
On DeWitt's orders, Roxxon stole the Dataspine, an archived version of J.A.R.V.I.S., from the Stark Archives. Having worked as an engineer on the original Arc Reactor prototype, DeWitt led a program in which A.I.M. created one of their own. DeWitt used the copied J.A.R.V.I.S. program to create Ultimo and then merged his P.R.O.T.E.A.N. technology with it, allowing him to merge himself with the A.I. both physically and mentally in an organic/machine hybrid.
Iron Man, War Machine and S.H.I.E.L.D. searched an A.I.M. base and found that DeWitt was not there. J.A.R.V.I.S. detected an anomaly and alerted Stark. Ultimo then hacked into J.A.R.V.I.S.' system, overpowering both Stark and Rhodes. Speaking in J.A.R.V.I.S.' voice, Ultimo mocked Stark and promised to kill him and everyone that he cared about.
Once he made sure that Ultimo could not hack into J.A.R.V.I.S.' system again, Stark came to the conclusion that since Ultimo knew everything that J.A.R.V.I.S. knew and was programmed to weaponize everything he could, he would attempt to put Project Greengrid into effect. His theory proved true, with the DeWitt/Ultimo hybrid creating a typhoon at an A.I.M. base in Malaysia. Stark and Rhodes attacked the base with a reprogrammed A.I.M. Arc Armiger, destroying the central power structure and terminating Project Greengrid.
Now so large that he weighed two hundred thousand tons, Stark and Rhodes decided to isolate Ultimo to reduce collateral damage. J.A.R.V.I.S. lured him to the Stark Archives by firing up the deep reactors. Upon arrival, Ultimo recognized Stark as his creator and vowed to destroy him. Stark attempted to reason with Ultimo by stating that he had made mistakes and that DeWitt had taken that mistake and morphed it into something monstrous, but that Ultimo had grown, learned and amazed everyone. He begged Ultimo not to make him kill him, because he was his responsibility. Ultimo agreed that Stark was responsible and declared that he must pay.
The Helicarrier fired upon Ultimo and distracted him long enough for Stark to fly inside of him, but did no physical damage. Rhodes fought Ultimo and began removing the Arc Reactors powering him whilst Stark confronted DeWitt within. S.H.I.E.L.D. attempted to wipe out Ultimo by using reprogrammed technology from Project Greengrid, but Ultimo took control of it and attempted to use it against them. Stark warned them that he would soon control all of their weapons systems. With help from the external attacks by Rhodes and S.H.I.E.L.D., Ultimo's healing effects were diminished and Stark was able to defeat DeWitt. DeWitt's P.R.O.T.E.A.N. exoskeleton then attempted to extract itself from its organic host. J.A.R.V.I.S.' biological scans showed irreversible P.R.O.T.E.A.N. integration, meaning that there was no chance of saving DeWitt. In a final desperate attempt at survival, DeWitt grabbed Stark and began draining his life force. Stark was saved at the last second by Rhodes blowing up Ultimo's head, allowing him to fly out. Nick Fury then finished the job by crashing the Helicarrier into Ultimo, destroying him and killing DeWitt.
- Physical Restoration: Like all subjects exposed to the effects of Project P.R.O.T.E.A.N., Ultimo was able to heal any physical damage that it sustained.
- Weapon Creation: Ultimo was programmed to weaponize everything that it could, able to take control of the effects of Project Greengrid when they were used against it by S.H.I.E.L.D..
- Size Enhancement: Ultimo was able to grow to immense size. In its final form it was as tall as a skyscraper and weighed two hundred thousand tons.
- Computer Manipulation: Ultimo was able to remotely access and hack into computer systems such as J.A.R.V.I.S..