Robert Downey Jr.'s Tony Stark, a.k.a. Iron Man, goes through a profound change after The Avengers, and this is reflected in one key area of filmmaking from Iron Man 3 onward. Tony starts out life as a selfish, almost antiheroic figure and slowly evolves into the man willing to make the ultimate sacrifice to kill Thanos using the Infinity Stones in Avengers: Endgame. The MCU cleverly demonstrates this change in one key shift in Tony's characterization.
Tony Stark clearly loves heavy rock music in the MCU and is defined by this in his Phase 1 appearances. Iron Man aptly concludes with Black Sabbath's «Iron Man» and also samples AC/DC's song «Back in Black.» Iron Man 2 features a whole album of AC/DC songs that are used in key scenes, such as when Tony enters the Stark Expo. The Avengers also briefly uses the song «Shoot to Thrill» as Iron Man dramatically appears to aid Captain America (Chris Evans) against Loki (Tom Hiddleston). Notably, the song is used in-universe rather than just for the audience's benefit, and Tony also wears a Black Sabbath T-shirt throughout the movie. However, after The Avengers, Tony Stark's Iron Man is solely defined by heroic orchestral scores, such as Brian Tyler's excellent Iron Man 3 soundtrack.
Related: Every Way The MCU Has Changed Iron Man's Story Since His Death
Phasing out AC/DC and Black Sabbath as key elements of Tony Stark's character is a great way to show his progression as a hero. The events of The Avengers have a profound impact on Tony, leading him to develop PTSD in Iron Man 3 and eventually build Ultron out of fear of threats from space in Avengers: Age of Ultron. As Tony becomes a more mature, if paranoid, superhero, it makes sense that he would stop indulging in fun music by
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