James Spader didn’t return as the incredibly powerful and dangerous A.I.
[Editor's note: The following contains spoilers for Marvel's What If…?, Season 1, Episode 8, “What If… Ultron Won?”]
Episode 8 of Marvel's What If…? featured something along the lines of breaking the fourth wall on a literal level, as our extremely observant pal the Watcher (Jeffrey Wright) chose to observe a universe where things went more horribly wrong than usual. In this realm, the highly advanced A.I. developed by Tony Stark to protect the planet Earth once again resorted to extreme measures to fulfill its purposes, but this time was a lot more successful: as the episode title establishes, Ultron beats the Avengers, and goes on to also attack the Watcher, having evolved to a high-enough level of consciousness to be aware of the existence of multiverses, not to mention the Watcher himself.