The Avengers have faced off against the worst enemies imaginable. That's part and parcel of the job when it comes to a team that has the nickname of Earth's Mightiest Heroes, but not all of their foes are created equally. Some Avengers villains talk a big game but are little more than cannon fodder. However, others make the team earn their victories because they're the deadliest foes around.
The Avengers have faced enemies who've committed atrocities on a truly massive scale. They've killed vast numbers of people not only on Earth, but across the universe. While the Avengers are actually pretty bad at avenging, they do their best to stop the most dangerous enemies in the universe before they claim more innocent lives.
10 Grim Reaper
Kill Count: 1,000+
Grim Reaper has made a mockery of death, resurrecting many times because of his mastery of necromancy. Eric Williams was always the black sheep of his family, using and abusing everyone to get his way. Grim Reaper embraced evil the way his brother Simon, the Avenger known as Wonder Man, embraced good. Death has no meaning anymore for Grim Reaper. It's a momentary stumbling block for him and he has no problem dealing it out.
A brutal killer, Grim Reaper's death toll is somewhere in the low thousands. His scythe is a powerful weapon, and it's allowed him to spread death on an unbelievable scale. As a necromancer, Grim Reaper lives and breathes death, and has done more than his share of killing during his long villainous career.
9 Hydra Supreme Captain America
Kill Count: 1,000+
Captain America was transformed into a Hydra agent by Kobik when she de-aged him, a legacy of the control that Red Skull had over her. This change turned Steve Rogers into the secret enemy of the people who thought he was their friend. Rogers enacted a plan that gave him control over the United States and revealed himself as Hydra Supreme.
As Hydra Supreme, Steve Rogers didn't personally kill a lot of people, but he ordered the death of untold thousands. Hydra Supreme Captain America took all the tactical skill he built up over the years and used it to fight for fascism. He was a murderous monster, and he believed the ends justified the means.
8 Baron Heinrich Zemo
Kill Count: 10,000+
The Avengers have fought two different Barons Zemo: Heinrich and his son Helmut. While Helmut has no qualms with killing, he definitely can't match his father's body count. Heinrich was a high-ranking Nazi officer, commanding Wehrmacht and Hydra soldiers in battle. This Baron Zemo sanctioned a staggering number of deaths, using the war machine of the Third Reich to destroy all who he considered inferior.
After the war, Heinrich went into hiding with Hydra and slaughtered even more people. Over the decades, it would be easy to assume that Heinrich killed tens of thousands, although most of those would have been in WWII. Heinrich was a monster, and the world was made a better place with his death.
7 Red Skull
Kill Count: 100,000+
Red Skull is a brutal monster and has been killing people for ages. His first murder came when he was just a child, which is how he got noticed by Hitler. Red Skull became the Third Reich's most feared soldier, and he did that by killing many people. He had power over the Wehrmacht and SS second only to Hitler, and Hydra was his own personal strike force.
Red Skull almost certainly was responsible for at least a hundred thousand deaths, if not more, and many of them at his own hands. His command of Hydra meant caused even more to die at his hands. Since the dawn of the age of heroes, Red Skull and his forces have killed many more, and events like releasing the Red Zone virus padded out his kill count. Red Skull is a prolific mass murderer and has been for decades.
6 Loki
Kill Count: 1,000,000+
Loki is the Avengers' first enemy. For thousands of years, Loki was the scourge of Asgard, their schemes to take the throne costing many lives. When Loki was in the good graces of Asgard, they fought alongside Thor, the Warriors Three, and Lady Sif. In those millennia, Loki killed many beings, both with their own hands and at their command.
Loki may not seem like they're a prolific killer, but life has always been cheap for Loki, except for their own. Loki has had entire armies at their command, ones which have done their murderous bidding and also been slaughtered by the forces of Asgard. It's hard to pinpoint Loki's exact kill count, but it's possibly in the millions.
5 Kang The Conqueror
Kill Count: 1,000,000+
Kang the Conqueror lives up to his name. Obsessed with the conquerors of the past, Kang outdid all of them. Kang spent years becoming the greatest warrior of the future, leading armies and taking the fighting into his hands. Kang has conquered planets and star systems, destroying entire civilizations in his mission to be the greatest conqueror that has ever existed.
Kang has killed millions of people over the years. Kang is an honorable warrior, and he has no problem with giving his opponents the death that warriors deserve. Despite not killing the Avengers — the goal that he thinks will make him the greatest ever — Kang is a killer of the highest order, forging an empire greater than any other.
4 Ultron
Kill Count: 1,000,000,000+
Ultron is a technological terror. The android hates all biological life and has set out to destroy all of it everywhere. For many years, he kept his predations confined to the Earth, killing millions. His biggest killing event was when he destroyed the country of Slorenia, slaughtering every living being in minutes. However, his greatest period of killing came when he took control of the Phalanx.
Now, the Phalanx mostly try to assimilate their victims, but even so, they have to battle their way through the defenses of the worlds they target. Ultron was responsible for somewhere around a billion deaths during this period, if not more. In Age o Ultron, Ultron smashed the defenses of the Earth and killed nearly every human on Earth. Ultron is a murderous monster.
3 The Apocalypse Twins
Kill Count: 7,000,000,000+
The Apocalypse Twins are the children of Archangel and Pestilence of the Final Horsemen. They were kidnapped by Kang the Conqueror, who wanted to use the powerful mutants in his own schemes. Kang started their training by leaving them in the mutant camps of a terrible future, where they would be tormented, learning that life was suffering. Kang would test them by taking them to kill people and then dropping them back in the camp.
The Apocalypse Twins broke away from Kang eventually and set out to create a paradise for mutants. They killed a Celestial, which brought the other Celestials to Earth. Heroes and villains alike tried to fight them off, but failed and the Earth was destroyed. The Apocalypse Twins killed over seven billion people with their plan, forcing the surviving Avengers to go back in time to stop them.
2 Thanos
Kill Count: 10,000,000,000+
Thanos is everyone's enemy, because he's a threat to the entire universe. Thanos started killing at a young age and his first mass casualty event was causing a nuclear holocaust on Titan, killing millions. That was only the beginning, though. Thanos traveled the universe, killing as many as he possibly could. Thanos is mostly known for using the Infinity Gauntlet to kill half of all life in the universe. Even if those murders are discounted because everyone was resurrected, he's still killed countless billions.
Thanos is possibly the most feared individual in the cosmos. Everyone knows what happens when Thanos shows up, and it's usually that many people die in the most terrible ways possible. Thanos is a mass murderer of the highest order, doing the vast majority of his killing completely on his own.
1 The Builders
Kill Count: 50,000,000,000+
The Builders are thought to be the oldest race in existence. For eons, the Builders have traveled the universe, creating and destroying entire species, building paths through the multiverse. When the Incursions began, the Builders decided it was time to pack it all in, and mobilized their Engineers and Alephs into a potent fighting force.
The Builder fleet made their way inexorably through the universe, destroying everything in their war and sparking an intergalactic war, as seen in the sci-fi epic Infinity. The Builders cut a bloody through space, on their way to Earth. They killed billions, and those they didn't kill, they conquered. Taking it all together, with their prior acts and their war, the Builders have easily outdone Thanos when it comes to kills, making them the Avengers' deadliest foes.