As the face of the Marvel Cinematic Universe, Iron Man has been one of the most influential characters in the franchise. He made several critical decisions that shaped the universe. Robert Downey Jr.'s Tony Stark was a prominent member of the Avengers despite almost not making the roster. While he wasn't the most powerful hero in the MCU, he was intrinsic in each of the Avengers' missions, including their biggest one fighting Thanos in Avengers: Infinity War and Avengers: Endgame.
https://screenrant.com/iron-man-tony-stark-choices-change-mcu/