The wait for a cinematic event over a decade in the making has come to an end. Over the course of the year-long wait for Avengers: Endgame, there was much speculation about how the Infinity Saga would draw to a close. Fans everywhere, this one included, oscillated between the events that that could occur from the moment Thanos snapped his fingers and wiped out half of life in the universe, and the Avengers reversing the effects. But there was one constant outcome: Tony Stark had to sacrifice himself to do it.
“You’re not the guy to make the sacrifice play, to lay down on a wire and let the other guy crawl over you”
From the moment he first donned the Iron Man suit Tony Stark has gone through various changes, but the heart of his character is still his motivation. He’d always been driven by guilt. He saw his life’s work developing weapons of war at Stark Industries and saw it merited nothing but destruction. In the face of that realization, he became a walking, talking deterrent. As new additions entered his life - his love Pepper Potts, Peter Parker - who was like a son to Tony - and countless others he cared for, his guilt continued to grow. When he felt he couldn’t do enough, he walked away, but even after initiating the Clean Slate Protocol in Iron Man 3 and destroying all his suits, he couldn’t shake what he knew was coming.
“I wasn’t tricked, I was shown. It wasn’t a nightmare, it was my legacy”
Tony’s legacy has been a running point of conversation since the MCU began, & it was never more important than in Avengers: Age of Ultron. The vision shown to him by Scarlet Witch gave him a look at the worst version of that legacy - one where The Avengers are dead, and Steve Rogers telling Tony he could have saved them. Tony, being the embodiment of noble arrogance, believed his inactions would destroy everything, clouding his judgment so badly that he stopped thinking about the repercussions of his actions. He wanted to leave behind a world that was safer because of him to calm the chaos that came at the hands of his weapons. He could never walk away.
“I hope they remember you.”
In the five years since Thanos’ snap, Tony settled down with Pepper and had a daughter, Morgan. He seemed to have moved on, accepted defeat & chose to embrace his second chance with his family. But he’s built new armor (Mark 85, the 85th Iron Man armor. The one in Infinity War is Mark 50), along with a surprise armored suit for Pepper. He can’t sleep when the Avengers inform them of their plan to retrieve the stones, so much he stays up all night figuring out how to make the “time heist” work. At the end of it all, he saw his chance to repair his legacy and restore the world he aimed to protect, and he needed to be there to see it through.