In one of the more shocking moments in recent Marvel Comics history, Captain Marvel was responsible for the demise of Iron Man in Civil War II. Carol Danvers' decision-making in the storyline remains one of the low-points of the character's past.
Civil War II by Brian Michael Bendis and Dave Marquez was released in 2016, around the same time as Captain America: Civil War film. While the movie saw Iron Man take on Captain America, Tony Stark took on Captain Marvel in the sequel to the original Marvel Civil War. This time around, the infighting was caused by a difference of opinions on what to do with a new Inhuman named Ulysses, who could predict the future. Captain Marvel wanted to use him to stop crimes before they happened, while Iron Man didn't quite agree with the philosophy.
Iron Man's frustrations with Carol were completely understandable. War Machine died and Captain Marvel was calling for the arrest of Miles Morales for killing Steve Rogers in one of Ulysses's visions. Carol didn't relent in wanting to bring Miles to justice for a crime he hadn't committed yet and Iron Man took issue, attacking Captain Marvel. In the epic fight, Captain Marvel didn't hold back and ultimately unleashed the full force of her power blasting Stark out of his super suit. Stark was put in a coma and survived only because of his own experiments on himself.
While Iron Man wouldn't disappear, Captain Marvel's decision still has a lasting impact on comics today. Stark would return, but not as his original self. He effectively became an artificial intelligence version of himself after being taken down by Captain Marvel. In Tony Stark: Iron Man #19, Tony still isn't ready to forgive Carol. Tony harbors understandable resentment towards Captain Marvel, as he puts it, it "turns out I'm just some lifelike copy that crawled out of a tube. The real Tony's been dead since you killed him."
Civil War II had some exciting moments, but ultimately, it did major damage to Captain Marvel and to her relationship with Iron Man. The somewhat villainous turn for Carol and her ease in betraying her closest allies because of Ulysses' visions was extremely out of character. Killing the former version of Tony Stark was icing on the cake that cemented the arc being one of the more forgettable for the popular superhero. Thankfully, Captain Marvel has been excelling in her own series. However, her relationship with Stark, even years later, isn't about to be repaired. The moment in Civil War II represents her biggest mistake - and nothing else is particularly close.