At the heart of "Avengers: Endgame" lies the concept of the Infinity Stones, powerful cosmic artifacts that grant their wielder unparalleled control over various aspects of existence. These stones had been featured throughout the MCU in different capacities, but they took center stage in "Avengers: Infinity War" (2018), the penultimate film in the saga. The villainous Thanos, portrayed by Josh Brolin, sought to collect all six Infinity Stones to carry out his plan of wiping out half of all life in the universe.

The stakes were raised to an unprecedented level, setting the stage for the emotional and action-packed conclusion that would follow in "Endgame." The stones became not only plot devices but also symbolic representations of the interconnectedness of the MCU itself.