This article contains spoilers for Doctor Strange in the Multiverse of Madness
Avengers: Endgame. Thanos was undoubtedly the biggest MCU villain of Phases 1 through 3, affecting a myriad of different films across the sprawling franchise. Rightfully then, Multiverse of Madness continues to include things relating to the Mad Titan that not only provide depth to the film itself but retroactively improve upon things from the MCU's past.
Since his introduction in the end-credits scene of and Avengers: Endgame. Across these two films, Thanos and his many powers granted by the Infinity Stones proved him a formidable opponent to almost every single character introduced in the MCU to that point. With Doctor Strange in the Multiverse of Madness, the threat of Thanos is built upon, despite his defeat at the hands of Tony Stark, in a way that improves one of the character's most iconic lines.
The line in question is Thanos' famous goad towards the Avengers: "I am inevitable". This was uttered by Thanos two different times in Endgame—once before he is killed by Thor at the beginning of the film, and again by the time-traveling Thanos towards the end of the film before being defeated by Iron Man. In Doctor Strange in the Multiverse of Madness, this memorable line is given even more meaning than simply referencing his Earth-616 motivations of eliminating half of all life throughout the universe. During Doctor Strange (Benedict Cumberbatch) and America Chavez's (Xochitl Gomez) visit to Earth-838, it is revealed that the Illuminati in that universe was formed to defeat their own version of the Mad Titan, Thanos.
Earlier in the film, Chavez also expresses surprise upon learning of Strange's role in defeating Thanos on Earth-616 (or, the Sacred Timeline), indicating that she was previously aware of the Mad Titan and his significant, universe-altering power. This revelation, in addition to Earth-838's Illuminati being formed in Doctor Strange 2 to fight Thanos, shows how big of a threat the villain is/has been to potentially every universe throughout the multiverse. This idea further builds upon characters like Classic Loki and the appearance of the Thanos-Copter in the Disney+ series Loki, which previously helped to establish Thanos' multiversal impact.
Therefore, Thanos' line of him being inevitable is only improved upon. Rather than just being about his success in using the Infinity Stones to carry out his goals, that line now indicates Thanos' inevitability across the entire multiverse. While Marvel has moved on from villains like Thanos, setting up MCU villains such as Kang the Conqueror and multiversal issues like incursions—established in Eternals may prove to be more powerful than Thanos going forward, the Mad Titan's line in Avengers: Endgame, and what this means in Doctor Strange in the Multiverse of Madness, proves his tenacity and dangerous dedication towards his beliefs extends across the vast multiverse.
