Warning: This article contains spoilers for What If...? episode 8.

Thanos looked incredibly weak in Ultron (voiced by Ross Marquand) loose on its heroes. After the evil AI successfully destroyed Earth, the villain sets sights on the rest of the MCU, taking up a mission to destroy the entire Multiverse. The Watcher (Jeffrey Wright) battled Ultron through various worlds, but he realizes he has no chance on his own. To save the Multiverse, the Watcher breaks his oath not to interfere and brings on the help of the evil Doctor Strange (Benedict Cumberbatch).

The first three phases of the MCU were all about Thanos (Josh Brolin). Ever since 2012's Avengers: Endgame, the villain gave Earth's Mightiest Heroes their first actual loss. Iron Man (Robert Downey Jr.) and Black Widow (Scarlett Johansson) even lost their lives to defeat him.

Related: Marvel Finally Made Age Of Ultron’s Title Make Sense

Though Thanos was the MCU's first real threat, What If...? episode 8 is all about Ultron. In the episode, Ultron's plans to destroy Earth finally work out just in time for Thanos to arrive with the Infinity Stones. "Fascinating," Ultron says after seeing Thanos step out of a portal. Then, without a second thought, Ultron uses the Mind Stone to slice Thanos in half and collect all the Infinity Stones. Considering how important Thanos was to the first decade of the MCU, the moment was shocking. However, there's an obvious reason for it.

What If...? episode 8 was all about establishing Ultron as the MCU's greatest threat. In the episode, Ultron eliminates life without mercy, thinking it's the only proper way to achieve peace. Immediately after destroying Earth, Ultron uses the Infinity Stones to take his mission to other worlds, destroying Asgard, Ego, and anything else in his path. The Watcher even breaks his vow in an effort to stop him. Ultron's level of villainy is unparalleled thus far in the MCU, and killing Thanos was an easy way to show that. After all, Thanos was previously the most significant threat for the Avengers, yet the Watcher obviously didn't bother interfering. For the Watcher to break his vow, the threat needs to be something unprecedented.

Thanos' death also serves as the MCU's way to move on. Following Infinity War and Endgame, Loki, Marvel revealed that the Infinity Stones aren't always so powerful after all, with the items being useless within the confines of the Time Variance Authority. Then, in What If...?, Marvel has repeatedly made Thanos weak, showing him fall victim to a zombie virus and having Ultron slice him in half instantly. It's all Marvel's way of bringing balance back to other villains of the MCU, and balance is ultimately something Thanos would appreciate.

More: Why Steve Rogers Is President In What If Episode 8 (& Not Fighting Ultron)

Marvel's What If...? releases new episodes Wednesdays on Disney+.

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