Phase 4 managed to bring back Ultron in a surprising way, showcasing the rogue AI in a brief appearance in Disney+'s What If...? animated series.
Ultron's appearance in What If...? led many to believe that the MCU villain will eventually return. However, the villain did make his live-action comeback recently, but it was in a non-canon sequence in Disney Cruise's Avengers: Quantum Encounter.
Marvel Studios Set to Bring Back Ultron
According to the "trusted sources" of the Tales from the mod queue from the Marvel Studios Spoilers subreddit, James Spader is set to reprise his MCU role as Ultron in Armor Wars.
Plot details of Armor Wars are unknown, meaning Ultron may or may not act as the main villain of the movie.
A past rumor hinted at Ultron's return, noting that the Avengers foe was not destroyed at the end of Age of Ultron and small shards of the program still remain "dormant" in the universe.
Spader last portrayed Ultron in MCU canon during 2015's Avengers: Age of Ultron.
Marvel Studios and Disney have not confirmed or commented on this.
How Ultron Will Return in Armor Wars (Theory)
Given Armor Wars is largely connected to Tony Stark's legacy, it isn't surprising that Ultron, a villain that he created, will return.
However, the big question remains: how will Ultron return in the Don Cheadle-led movie happen?
At the end of Avengers: Age of Ultron, Vision destroyed the last Ultron bot, indicating that the rogue AI was defeated. However, the villain being an AI could be the key to his comeback.
Considering a past rumor shared that small shards of Ultron remain dormant, it's possible that whoever is meddling with Stark's technology in Armor Wars might've accidentally or even purposively activated the villain to kickstart his return.
A minor Easter egg in Spider-Man: Homecoming revealed that the Department of Damage Control has a head of an Ultron bot. Given that the group is rumored to return in Armor Wars, there's a chance that this broken Ultron bot could act as the means of James Spader's MCU return.
Whatever the case, Ultron's return spells trouble for the remaining Avengers, especially now that Tony Stark is gone.
Marvel Studios has yet to announce Armor Wars' release date.