The Marvel Cinematic Universe has finally moved on from Iron Man and his sacrifice at the end of Avengers: Endgame, but this universe still has one big mystery from Iron Man 3 to solve. Robert Downey Jr’s Iron Man is the hero that kicked off the MCU as it’s known, and as such, he was one of the leaders of this connected universe throughout the Infinity Saga, even leading the original Avengers team alongside Captain America. Iron Man was also the first superhero to get three solo movies in the MCU, setting the model for the rest of this universe’s characters, but his sequels didn’t really match the quality and success of his debut movie.
https://screenrant.com/mcu-iron-man-3-extremis-mystery-forgot/