The cybernetic menace known as Ultron, created by the mind of genius scientist Hank Pym, aka Ant-Man, refers to himself as the Avengers' greatest threat. The vast array of weapons he's employed over the years include adamantium bodies, a nuclear reactor, and technorganic viruses capable of infecting entire planets. However, he has seldom used his most powerful weapon, one that could end any fight in an instant.
Ultron began as an experiment in AI that quickly went wrong. He developed a conscious mind, but one that was filled with hate and contempt for his "father" and, by extension, Earth's Mightiest Heroes. Far from being just a rogue robot, Ultron is responsible for slaughtering thousands of people on Earth, and millions across the galaxy. However, he has never managed to attain his goal of destroying the Avengers or replacing all organic life with his creations
Ultron's most powerful weapon is probably the very first one he ever used: the encephalo-beam. Located in his head, this ray allows him to plunge his victims into a death-like coma, and then hypnotize them and outright control their actions. He used it to erase Pym's memory right after being created, brainwashing him into forgetting Ultron existed. Despite how powerful the weapon is, however, he has used it only a handful of times, most notably to hypnotize Jarvis, which almost led to the complete annihilation of the Avengers.
But Ultron's desire to control others and harm the Avengers isn't merely a product of his own obsession. In Avengers: Rage of Ultron by Rick Remender, Jerome Opeña, Pepe Larraz and Mark Morales, after a long period of isolation on Titan, Ultron discovers Ant-Man's memories inside his systems. He becomes aware of Hank Pym's subconscious hatred for humanity, thus establishing that all the atrocities he committed were a dark reflection of his creator's worst impulses.
Confronted with these facts, Pym its, "I punished you for being exactly what I made you to be. My reflection." What Ultron saw in Hank's memories was a man who grew up feeling misunderstood and rejected by the world, his consuming self-doubt slowly coalescing into hatred for all humanity, the same hatred shared by his creation. Finding himself in a group of larger than life superheroes, Hank felt suffocated and overwhelmed, and Ultron's hatred of the group is partly based on this feeling - a low moment for Hank, but the core of Ultron's being. It's no coincidence that Ultron wields the encephalo-beam, but rather an expression of the desire he feels to control those around him; a desire that comes from the former Ant-Man.
At the same time, this twisted relationship between "father" and "son" may explain why Ultron hardly uses the weapon, rejecting Hank's desire to be accepted by the Avengers and humanity at large. Ultron is without a doubt one of Marvel's iconic villains, not just due to the threat he poses to the world, but because of the ways his very personal desire to break and control the Avenger stems from his twisted relationship with his creator, Ant-Man.
