Robert Downey Jr.'s portrayal of Tony Stark in the Avengers: Endgame.
Though Black Widow, the longevity of his time as Tony Stark and the sense of fulfillment the totality of his performance brought ensures that his time as Iron Man will remain a hallmark of the superhero genre for decades to come. However, despite the widespread adoration for his portrayal of Marvel's arrogant but lovable tech-savvy Avenger, the MCU overlooked a key aspect of his comic book origins: the MCU never took a real dive into Tony Stark's alcoholism.
There were hints early on that the MCU would go in this direction, specifically in Avengers: Infinity War. However, a full exploration of Tony's drinking and hard-living ways never received full play in the MCU.
The absence of Tony's alcoholism still leaves a significant corner of his story unexplored and one that now never will be after his death in Endgame. Viewed in the context of his complete MCU story now, due to what Tony's thinks are the final days of his life from the palladium poisoning, Tony's drunken meltdown in Iron Man 2 is more of a hastened mid-life crisis than a true example of alcoholism. As with the side effects of swapping Edward Norton for Mark Ruffalo as Bruce Banner, the MCU's family-friendly approach under the Disney umbrella has seen the franchise make numerous trade-offs in the kinds of stories it's been able to tell, and sacrificing Tony's alcoholism is unfortunately among them.
The lack of Tony binge-drinking doesn't undercut the effect that Robert Downey Jr.'s performance has had on the MCU. In fact, Downey was such a pillar of the MCU for so long that the franchise is undoubtedly in uncharted waters with his retirement. Nevertheless, the fact that Tony Stark's alcoholism was never truly integrated into his story will always be the biggest element of his history that the Marvel Cinematic Universe never explored.
