The MCU Hero With The Highest Kill Count Is Probably Not Who Marvel Fans Think
Action movies always come with some kind of kill count, not just for villains but also for heroes. Jason Bourne doesn't hesitate to kill to survive. Bryan Mills uses his particular set of skills to take out dozens of armed opponents in "Taken." Luke Skywalker's kill count trumps Darth Vader's (thanks to the Death Star). Even Disney princesses like Mulan get in on the morbid kill count action.
But what about the Marvel Cinematic Universe? The MCU is filled with action-packed sequences, many of which leave a serious body count. Villain-wise, Thanos is an obvious winner, since he snaps half the galaxy away. But what about the hero with the biggest kill count? It's Tony Stark, and the reason is as obvious as Thanos'. Stark uses the Infinity Gauntlet on Thanos' army. He also uses a nuclear missile on the Dark Lord's armada in "The Avengers."
One estimate, from the List of Deaths Wiki, puts the Iron Avenger's kill count at 75,350. However, it's worth noting that 75,127 of these come from "The Avengers" and it doesn't take into account the snapped-away victims in "Avengers: Endgame." Another list, from the Killcounts Wiki, does the opposite, using the same total number but suggesting 74,999 deaths in "Endgame" and not counting the nuclear strike in "The Avengers." In either case, the death count comes up tens of thousands short and should probably be closer to the 150,000 mark. Between nuclear missiles and an Infinity Gauntlet, Stark's kill capacity is unmatched. No other hero uses that kind of power to eliminate so much life in such a sudden and targeted manner.
What other heroes have high kill counts?
It's no secret that Tony Stark isn't alone in his violent life-taking efforts. Plenty of other heroes have recklessly spilled blood throughout their careers. If you take the animated portion of the MCU into account, then you have to give Strange Supreme the nod. The universe-ending "What If...?" character has a kill count that stands at around seven and a half billion.
After that outlier, things settle down to more Stark-like numbers. Thor, for instance, admits to 3,000 kills in his "Infinity War" estimate, saying, "I'm 1,500 years old. I've killed twice as many enemies as that." Redditor u/plopkind makes the case that Steve Rogers' Captain America likely killed 3,000 people on the helicarriers in "Captain America: Winter Soldier" (and that doesn't include unknown victims beneath the behemoths as they crashed). Quora user Lee Alexander also makes a compelling argument that Hulk may have the most overall kills due to his unknown time fighting as a gladiator on Sakaar. Alexander's estimate there? Upward of 20,000 victims in 366 years.
Another aspect to consider here is direct versus indirect kills. What if someone orders a kill but doesn't actually pull the trigger? You know who we're talking about. If you trace many of these body counts back far enough, you end up at the doorstep of one man: Nick Fury. Fury may be out for the greater good, but through the recruitment and organization of the Avengers alone (let alone his other initiatives), he is indirectly responsible for hundreds of thousands of deaths.
One hero clearly has the highest life count, too
It's worth noting that not all Avengers are hellbent on killing their adversaries and leaving a wake of destruction in their path. These are heroes for a reason, and some of them have a remarkable track record for not just saving but restoring life. This traces right back to our original reason for the highest MCU kill count.
In the same way that the Tony Stark Infinity Gauntlet trump card gives him the highest kill count, the overpowered arm-piece provides the answer to the antithesis of the question. There are various life-giving moments in the MCU, such as the work of the Celestials. One could even argue that Vision's birth is a sort of creation moment, as is that of Ultron (both of which put Tony Stark into the mix again — even if Ultron is admittedly one of Stark's biggest mistakes). But the Infinity Gauntlet once again settles the matter, as Professor Hulk's reverse snap has to be, hands down, the biggest sudden surge of life across the universe.
Ironically, Hulk is an Avenger with some of the most blood on his hands. Yet his calm, cerebral alternate iteration gives the universe a fresh lease on life by reversing the Thanos-induced damage of the Snap. It just goes to show, you never know what kind of curveball is going to come next in this quirky, inspiring, and blood-soaked superhero universe.