Despite being ranked higher in the Marvel Cinematic Universe, Loki could not stand up to Ultron in the comics. In a way, this defeat is one of the worst fates that can be imagined for the Asgardian.
In a one on one fight in a random encounter, Ultron 8 out of 10 times. Though these fights don't always happen. If there were to have prepration, Ultron would get a more advanced technology but Loki, would fool the nine realms tricking them all into thinking he was their leader.
Just as Thor or his Rune King version can easily defeat Ultron, Shazam (Billy Batson) shouldn't have any problem doing the same. Shazam's powers are magical and something Ultron might have difficulty processing.
In the MCU, no. Contrary to the comics, Thor is horrendously nerfed on the big screen. Because of this, his strength and size pale in comparison to his comic counterpart. This was why Ultron managed to take on all of the Avengers — for the sake of the movie.
Ultron is extremely powerful but Thanos is pretty much next level. While he couldn't pierce Ultron's adamantium shell, he would eventually be able to figure out a way to hurt Ultron even though he is composed of the indestructible metal.
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.
Ultron overpowering The Watcher With his vibranium body backed up by the Mind Stone's power, Ultron possessed an unfathomable amount of sheer strength, being able to defeat some of the strongest heroes in the universe such as Thor and Hulk.
A machine can pick up the weapon and move it anywhere since it's mindless and incapable of possessing the morals necessary to be considered worthy. By this logic, Ultron himself could have lifted it, but it wouldn't have done him much good.
Spider-Man has defeated enemies who are technically more powerful than Ultron, but the villain's adamantium body is nigh-indestructible. Unable to pierce Ultron's armor, Spider-Man will be at a serious disadvantage unless he can quickly come up with a solution — like calling in the Avengers.
Ultron is one of the Avengers' greatest foes and his destructive rampages have been stopped by the team every time. Cap has been a part of those battles, but his part was mostly as the team leader. Anytime he tried to fight Ultron on his own, he was quickly dispatched by the android.
However, Ultron's control over the Infinity Stones and the power he exhibited during his battle with The Watcher puts him on an entirely different level that could take out Galactus and his heralds.
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.
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. The evil A.I. has a particular dislike for Vision who inhabits the powerful body Ultron had built for himself.
Loki tries to use his abilities as a trickster god to turn on Thanos and kill him, but Thanos quickly stops his arm and breaks his neck. After Thanos kills him, that Loki's MCU run is over.
Next was Thor, Loki's brother, hoping this would be the last time they fought. Thor's Mjølnir and Loki's Scepter clashed. A bolt of lightning came down, knocking out Loki.
In the first "Thor" movie, Thor defeats Loki and stops him from taking the throne of Asgard. In "The Avengers," Thor captures Loki and brings him back to Asgard. In "Thor: Ragnarok," Thor exposes Loki's trickery and makes him help find their father, Odin.
In effortlessly taking down Iron Man and Thor, Ultron proved that MCU fans only saw his early forms, and not the immense potential he has to be the one who finally ends the Avengers not through trickery or betrayal, but by overpowering Earth's Mightiest Heroes two at a time.
Doctor Doom, the only threat to Ultron, used his time machine to assemble a team of Avengers from across history to help liberate the planet from Ultron's rule, culminating in the temporally-displaced Avengers defeating Ultron and convincing Doom–in reality a Doombot that worked with the Avengers A.I.
Hank should have destroyed his creation at once, when it began speaking before he'd even turned the machine on. Overpowering and mesmerizing Pym, the robot—which soon dubbed itself Ultron—hypnotically commanded Pym to forget its existence and abandon the New Jersey lab where it was created.
Loki is confirmed to be worthy of lifting Thor's hammer, Mjolnir, for the first time in official Marvel canon. In The Immortal Thor #5, Loki confidently catches and wields the hammer, showcasing his growth and heroism.
In the end, Deadpool wasn't worthy. While he seemingly had control of Mjolnir and the strength of Thor, it was all a mirage put on by Loki to distract Thor.
Jarvis doesn't lift Thor's Hammer. Jarvis is an AI. Vision lifts Thor's Hammer. Vision is still very new, freshly created, and hasn't done anything yet that would not make him worthy.
Thor joined forces with Firelord to prevent the end of everything. However, it took some upgraded armor and weapons for Thor to prevail over Thanos, who seemingly perished at the end of the story.
Wanda's hexes are no match for Thor's raw strength or his own magic, but with enough prep time to conjure the proper spell, Wanda could make Thor temporarily unworthy of Mjolnir by manipulating his memories or history. Without Mjolnir's power, Thor is significantly weakened, and therefore much more vulnerable.
Thanos didn't appear to have a hand in Ultron's creation, but it could be revealed in a future MCU film. Thanos saying “I'll do it myself” is most likely him angry with the failures of Loki from Avengers 1 and Ronan from Guardians of the Galaxy Vol 1.
