Vision Quest will reveal the key reason behind Ultron's return. Creator Terry Matalas confirmed that Vision did not completely destroy Ultron back then, but instead backed him up within his own mindscape.
When the series was first announced, it was widely believed that the story would follow WandaVision, explaining where White Vision went after leaving and whether regaining his memories meant he had become the original Vision. The trailer confirmed that these questions will be addressed, with Vision questioning his identity and whether he ever truly had a family.
The connections between Billy, Tommy, Wanda, and Vision will also be part of the plot, with Tommy playing an important role. However, Vision Quest is not solely focused on White Vision's identity; the trailer also confirms the return of Ultron from Avengers: Age of Ultron, with multiple AI characters appearing in human form.
These characters' activities are tied to Vision's "mindscape." In the trailer, Ultron even appears before Tommy in a grandfather-like figure, further indicating that he will not just make a brief appearance in the new storyline.
Matalas explained that Ultron was imprisoned in a New York loft-like area within Vision's mindscape. At the end of Avengers: Age of Ultron, Vision did not ruthlessly kill Ultron but chose to back him up, as Vision was always unwilling to truly destroy him.
This setting reinterprets Ultron's previously seemingly destroyed ending, creating a more direct link between Vision and Ultron's subsequent actions. According to the creator's current statements, Ultron seems to have changed, no longer attempting to conquer the world or eradicate humanity; Vision's decision to preserve his consciousness aligns with his character trait of not wanting to leave no survivors.