When was the mcu multiverse introduced?

The concept of a multiverse—a collection of infinite alternate realities—was first explored in the MCU in the 2016 film *Doctor Strange*. In that film, the character Stephen Strange encounters the Time Stone and learns that reality is not fixed, setting the stage for the multiverse narrative. The multiverse is revisited in *Avengers: Endgame* (2019) when the Infinity Stones’ power is used to create new timelines. From Phase Four onward, the multiverse becomes a central storyline, culminating in the so‑called 'Multiverse Saga' that spans Phases Four, Five, and Six. The multiverse narrative revolves around the 'Sacred Timeline' and the Time Variance Authority (TVA), with key events such as Sylvie’s killing of the TVA’s leader, 'He Who Remains', further expanding the multiverse concept.