There were plenty of mysteries to resolve in Avengers: Endgame, but one of the biggest was who would get the honor of killing Thanos. He was the main baddie of the entire Infinity Saga, so defeating him would position one hero as the greatest in the Marvel Cinematic Universe to date.
Ultimately, this title goes to Tony Stark's Iron Man. Wielding all five Infinity Stones, he gives his life to kill Thanos and save the earth he's spent fifteen years fighting to protect. However, there are other heroes who arguably had much more to personally gain from taking down the Mad Titan.
Carol Danvers (Captain Marvel)
It's not a stretch to say Carol could kill an Infinity Gauntlet-free Thanos. She tries her best to overpower him in Avengers: Endgame, driven by what viewers at the time assumed was just a duty to protect the galaxy.
Then came WandaVision. While it's still unclear how much Carol was involved in Maria and Monica Rambeau's lives at this point, the show reveals Maria passed away while Monica was dusted and unable to say goodbye. It isn't a unique situation considering how many people suffered thanks to the Snap, but Thanos still shattered the only semblance of a real family Carol has in the MCU.
Clint Barton (Hawkeye)
Clint suffers an incredible tragedy when all four other members of his family fall into the half of the universe wiped out by Thanos. Hawkeye isn't the only one but copes worse than most by embarking on a murderous tear as his new alter-ego, Ronin — and that's all before Natasha dies on Vormir.
While he definitely isn't Thanos' biggest victim, Clint represents what happened to every family across the globe at the villain's hand. To see the closest thing the Avengers have to an everyman kill the greatest threat in the universe (at least at that point) would send a strong message about the power of humanity, even in the face of a Titan.
Natasha Romanoff (Black Widow)
Natasha's sacrifice for the Soul Stone is controversial, and many believe it should have been Hawkeye who (quite literally) took the fall instead. This belief strengthened with the release of Black Widow where Natasha proves how hard she's fought to shake off her dark history, only for her to die not long after.
The most iconic way to prove Natasha's hero status — mostly to herself — would have been for her to kill Thanos. True, she didn't have the strongest personal vendetta, but he did ultimately take away her second family just when they'd reunited once again and she'd refound her purpose.
Loki
Thanos has just slaughtered half of Asgard when he kills Loki in the opening scene of Avengers: Infinity War, which is already enough to warrant revenge. But that wasn't the first time the pair met. Thanos facilitated Loki's attack on New York in The Avengers, lending him his army of Chitauri and promising him Earth for the Tesseract.
Although Loki definitely wasn't an unwilling participant, it was this act that really cemented his status as a villain in his brother's eyes. Nothing could have marked his transformation from villain to hero like killing the big bad of the Infinity Saga.
Peter Quill (Star-Lord)
Admittedly, it's Peter's fault Thanos needed to be killed in the first place. Star-Lord's actions in Infinity War got a lot of flack when, upon realizing Thanos sacrificed Gamora for the Soul Stone, he attacks the Mad Titan just as the rest of the group are about to strip him of the Infinity Gauntlet.
All of this, however, comes from a place of grief. Not only does Thanos kill the woman Peter loves, but he is also the person who slaughtered half her planet (including her parents) and decades of torture. Peter proves time and time again how much he is driven by his heart, so killing the person responsible for breaking it just makes sense.
Drax
Actor Dave Bautista has lamented the fact that his character Drax wasn't the one to end Thanos. He has a point — from his first appearance in the MCU, Drax makes it clear that he is driven by a thirst for revenge upon Thanos for killing his wife, Ovette, and their daughter, Kamaria.
This is a key plot point in Guardians of the Galaxy but seems to have been dropped in favor of using Drax for comic relief ever since. Although he tries to rush Thanos early in Infinity War, he's never given a fair shot. While logically, Drax isn't strong enough to take on a gauntleted Thanos, it's frustrating that his character arc will never get its most satisfying conclusion.
Wanda Maximoff (Scarlet Witch)
The 2014 version of Thanos in Endgame doesn't know Wanda yet, but she definitely knows him. In his efforts to claim all the Infinity Stones, Thanos is the one who forces her to both kill Vision and witness him being murdered in the span of just a few seconds.
Wanda had already experienced her fair share of loss before this point and, as shown in WandaVision, this incident is her breaking point. Not only did Thanos kill half of one of the MCU's best couples for his own tyrannical cause, but he stole Wanda's planned future of growing old in the suburbs like a regular person.
Thor
Technically, Thor does kill Thanos in Endgame. However, this is just a weakened version of the villain, who is no longer bolstered by Infinity Stones having destroyed them after culling half the universe.
The rest of the movie sees Thor wallow in an identity crisis. He's always struggled with his self-worth, and while he does reach some semblance of his old self just before the final battle, his confidence still isn't there. After the loss of his mother, father, brother, best friend, and half his realm, defeating Thanos for good is a win Thor needed more than anyone.
Gamora
He may be her adoptive father, but Thanos is the reason Gamora has one of the most tragic backstories of all the Guardians. After killing her family, he abducted Gamora from her home planet (half of which he also killed) and transformed her into the "deadliest woman in the galaxy" before ultimately sacrificing her for the Soul Stone.
The return of Gamora's past self in Endgame could have been the ideal set-up for Thanos' downfall. As the only person he truly loves, she is his biggest weakness and her betrayal is what would hurt him the most. After all the pain Thanos has caused, that was what he really deserved.
Nebula
Nobody has earned the right to kill Thanos like Nebula. As one of his adopted children, she carried out endless dirty work but never benefited from the same favoritism as Gamora. Instead, Nebula was tortured and suffered more direct cruelty from Thanos's hand than any other character.
Considering her goal has always been to defeat him, defeating Thanos is the poetic justice Nebula deserved. He is the person responsible for making her the killing machine she is today, and this would have been the neatest ending to one of the MCU's best redemption arcs.