Warning: This article contains spoilers for What If...? episode 7.
Ultron returned to the Marvel Cinematic Universe in Frigga (voiced by Josette Eales), is away. Thor gathers many notable characters from throughout the MCU for the party, including Nebula (Karen Gillan), Grandmaster (Jeff Goldblum), and even Howard the Duck (Seth Green). However, Thor's partying can lead to planet-ending consequences, so eventually, Jane Foster (Natalie Portman) calls Thor's mom, and the partying has to come to an end.
The Watcher (Jeffrey Wright) is the one constant throughout What If...?. The character serves as the god-like narrator for the series, watching the events of the Multiverse from afar and vowing never to make himself part of the equation. "I observe all that transpires here, but I do not, cannot, will not interfere," the Watcher says in the series premiere. Over and over again, the Watcher refrains from interfering while disasters occur in different timelines in the Multiverse. Thus far, the character has remained true to his word. He observes but never gets involved.
In What If...? episode 7, a surprise return shocks the Watcher. After Thor and Jane set up their first date, the Watcher monologues from afar, saying, "They lived happily ever after." Then something snaps him back to reality. "Wait, what?" the Watcher says. Ultron, seemingly inhabiting Vision's body and wielding all six Infinity Stones, arrives with robot troops to face Thor. "Oh, dear. Perhaps I spoke too soon," the Watcher says, clearly not expecting the unwelcome party crashers. The Watcher is flabbergasted, and there's a reason why.
The moment changes What If...?. Though the Watcher has allowed various disasters to occur in different MCU timelines, Ultron and his Infinity Stones present a unique villain. Throughout the episode, Thor's actions were relatively innocuous and wouldn't necessarily as a threat significant enough to lead to the creation of Ultron. Thus, this version of Ultron likely isn't from Party Thor's universe. Because of that, Ultron is a Multiversal threat that could put the entire MCU in jeopardy. It's the most significant threat the series has introduced thus far.
With the new threat, it appears the Watcher will finally break his solemn rule. Thus far, the Watcher has been content watching tragedies unfold as long as they only affect their own universe. In episode 4, he even sits idly by as an evil Doctor Strange (Benedict Cumberbatch) destroys his world. But this is something different. Ultron is a threat to the entire Multiverse, not just the villain's own timeline. Because of this, the character's surprise appearance seems to be enough to get the Watcher involved finally. The Watcher interferes with the stories in Marvel's comics, so there's already a precedent for him to affect things. With the entire Multiverse in trouble, he can't simply sit by and watch.
Marvel's What If...? releases new episodes Wednesdays on Disney+