The following contains spoilers for Black Panther: Wakanda Forever, now in theaters.
A large aspect of the Marvel Cinematic Universe involves its heroes rectifying their own mistakes or fixing the problems of others close to them. Whether it be Shang-Chi trying to save his father from continuing a streak of violence or T'Challa making Wakanda a public nation, there's always something to be done to change mistakes. Perhaps the biggest example is Tony Stark's mistake of creating the AI, Ultron, without clearing it with his team. Because of this, he nearly ended the planet when Ultron gained sentience and concluded that humanity needed to be eradicated.
While Ultron was soundly defeated in Avengers: Age of Ultron, some theories have floated around that claim that his defeat was merely a postponement of a larger plan. That was best teased in a passing line in Black Panther: Wakanda Forever that Shuri's AI Griot could be one of many that could one day destroy the Earth. In passing, it's a funny comment about the older generation being wary of technology, but there are some solid grounds for concern. But while the line was meant to be a sweet moment for a mother and daughter, it could tease a return of Ultron, who's been planning a secret invasion for a decade.
The MCU's Ultron Has Been Working in the Shadows
When Ultron was defeated, the first step to this was having Vision cut the AI off from the rest of the web. That was so that his consciousness couldn't hide on the internet and escape to a new location. After that, the team had to destroy every drone, including Ultron himself, to ensure he couldn't return. While this worked, for the most part, the damage was done as his actions of Sokovia changed the world forever. But how could Ultron return when his ending was seemingly so definitive?
The reason for this involves Griot and AI as a whole. Essentially, Ultron would've likely foreseen that The Avengers would find a way to stop him after his Vision body got taken from him. To avoid his end, it's possible he hid a copy of himself somewhere on the web that was designed to gather data and slowly gain strength over time. With how turbulent the world was in the MCU following his defeat, this would allow the new, updated Ultron to be even more intelligent and conniving than ever. But this was only the first phase of his plan as the moment he gained enough strength and information, he would be able to turn most AI, like Griot, on their users and create a sneak attack on the internet, based in Wakanda.
Ultron Could Turn the World Further Against Wakanda
Having Ultron's actions based in Wakanda would make it seem like the nation had launched a highly detailed internet strike on the world. Considering how advanced the country is, it would make the world believe they masterminded it and further fuel the flames of war. Then, with the world now at Wakanda's throat, it wouldn't be able to uncover that Ultron was behind everything. With the AI left to roam free, he could then use the vibranium ore to create a new body that's indestructible and improved from what came before.
To make matters worse, only the Hulk, Thor and Hawkeye are alive to know what Ultron is capable of, but aside from that, this new generation of heroes may not know how to beat him. As a result, it would be like fighting him for the first time. But being that this was Ultron's plan all along, it would further cement him as one of the MCU's greatest enemies, not for his strength but his terrifying ability to plan ahead.
See Wakanda's AI in action in Black Panther: Wakanda Forever, now in theaters.