But if you want to know why he came so close, it's because he is a far more advanced AI than Jarvis. Jarvis was created just from Tony's genius, nothing more. Ultron was created using the sentience of an Infinity Stone, the Mind Stone. His AI is faster-learning and arguably smarter than any human mind.
During the Ultron Offensive, J.A.R.V.I.S. was destroyed by Ultron, although his remaining programming codes unknowingly continued to thwart Ultron's plans of gaining access to nuclear missiles.
Jarvis in the MCU is an extremely refined program, he has a definite limit, it's just that we aren't clearly shown what it is, and it's what stops him from being an actual consciousness like Ultron who is described as capable of thinking for himself.
Voiced by Paul Bettany, the AI was created by Tony to function as his main assistant. Being extremely secretive and cautious, JARVIS also served as Iron Man's company and even his friend. So when JARVIS was essentially killed by the corrupted Ultron in Avengers: Age of Ultron, Tony was understandably distraught.
JARVIS stands for Just A Rather Very Intelligent System. Tony Stark's trusty virtual butler Jarvis is the perfect assistant that can do everything from controlling Stark's home to providing him with information and assisting Stark run his business, his mansion, his tower and his Iron Man suits.
AVENGERS: Why Ultron Was Right (And Knew About The Scarlet Witch!)
Can cyborg hack Jarvis?
Cyborg would have no problem hacking JARVIS. Whatever it may be, JARVIS's system is still primitive compared to Cyborg. Cyborg is an interface of a Human and a mother box. The mother box is a sentient, intelligent alien computer used by the new gods.
He is a self-aware and highly intelligent artificial intelligence who develops a god complex and a grudge against his creator Hank Pym. His goal to destroy humanity in a shortsighted attempt at creating world peace has brought him into repeated conflict with the Avengers.
Ultron sees the Avengers as one of the main problems with the world's stunted evolution. He particularly dislikes his maker Tony Stark and flies into a rage when compared to him.
Paul Bettany portrays Vision. Prior to the introduction of Vision in the MCU, Paul Bettany had voiced J.A.R.V.I.S., Tony Stark's A.I. companion in previous films. Bettany admitted that he had little idea of what the role was, even as he recorded it, simply doing it as a favor for Jon Favreau.
Tony said he saw "a suit of armor around the world," and that he needed Ultron to run the Iron Legion. But JARVIS was already doing a pretty decent job of that, and he didn't seem to have reached the height of his capabilities.
The combination of the vibranium and the cosmic energy from the Mind Stone embedded in his forehead not only gave him life and immense intelligence, but also granted Ultron an extremely large number of superhuman capabilities.
In Marvel's What If…?, Ultron used the Mind Stone to instantly bisect Thanos before the two could properly fight. In a fight without any Infinity Stones, however, Thanos would destroy Ultron, further cementing him as one of the MCU's deadliest threats.
The technology of Ultron is so powerful that two of the most dangerous Avengers can get insta-killed casually without either seeing it coming. Ultron defeated both She-Hulk and the Hulk not by outsmarting them or even besting them in a real one-on-one fight, but by overwhelming them both with his strength.
Iron Man was able to more or less hold his own with Ultron. And Thor was more than capable of holding his own against both Iron Man and Captain America. So the only reason why Ultron was able to manhandle Thor was a story reason to set up Vision hitting Ultron with Mjolnir.
Fighting Captain Marvel is essentially like fighting a living embodiment of the Space Stone, but Ultron owned the real thing as well as the other five Infinity St0nes.
At the time Avengers: Age of Ultron was in production, the rights to Spider-Man were still being negotiated, so it wouldn't have been possible to add him.
This campy attitude failed hard, as Ultron's attempts to be a foreboding figure fell flat, given viewers saw him crack jokes earlier. Unlike characters like Thanos who never had any comedic quality, or Loki whose characterization was that of a spoiled brat, Ultron's hammy nature was far too uneven to be charming.
Trivia. So far, Infinity Ultron is the only villain from the Disney+ Marvel Cinematic Universe shows to be Pure Evil. He is also the only animated MCU villain to be Pure Evil, as What If...? is the franchise's first animated production ever.
What Makes Him Pure Evil? He betrayed his creator Pym mere moments after being created, quickly deemed humanity as flawed and has made numerous attempts to wipe out the entire race. He attempted to destroy any of his own creations, such as Vision and Jocasta, when they rebelled against him.
Moments before Vision destroyed him, Vision pointed out that Ultron was afraid of death, to which Ultron didn't even bother to deny as he admitted that he was afraid of Vision despite standing up to him.
In a single scene in Infinity War, Shuri proves that she's smarter than Bruce, and the rest of her work proves that she's got the edge over Tony more generally. Of course, it helps that she grew up in a virtual tech utopia. But Shuri would be one of the smartest people in the MCU regardless of where she's from.
When it comes to the smartest Avenger, it has to be Iron-Man that is considered to be the most intelligent. While he and Bruce Banner are likely on a level when it comes to their scientific knowledge, the fact that he retains that when turning into Iron-Man just edges him above the big green guy.
