Jonathan Majors' Kang The Conqueror is officially in the Marvel Cinematic Universe, and while we got just a taste of what he's like in Loki, we'll get to see a whole lot more of him in Ant-Man And The Wasp: Quantamania. Honestly, it's likely we'll see a whole lot more of him after that, so perhaps it's best to lay out just how dangerous this villain is since looks can be deceiving.
Kang may look like a substantially weaker MCU big bad than Thanos, but his command over time has allowed him to do some pretty horrific things throughout the history of Marvel Comics. It's hard to really top erasing half of existence, though there are a few things on this list I'd argue are just a little bit worse in the grand scheme of things.
Kang Tried To Murder Most Of The Avengers When They Were Infants
One time Vision decided to put an end to Kang once and for all, but in the process caused a paradox that created infinitely more problems for the Avengers than Kang ever did. The versions of Kang that survived via the paradox got together and proceeded to use their command over time to visit each and every Avenger as infants and attempt to murder them.
Weirdly enough, these Kangs were actually thwarted by a future version of Kang, who stuck most of the Avengers in limbo. Sure, the baby Avengers were ultimately spared and it was mostly Vision's fault the whole ordeal even happened. Still, the fact that Kang variants openly considered murdering a vast number of babies simply as a means of vengeance just shows how dark this character can go, and how easily he can mess up someone's life if he really wants to.
Kang Destroyed Washington D.C.
In one plot to invade the Earth, Kang and his son Marcus sought out some backup. In a masterful ploy, he offered any villain willing to aide in his conquering of Earth a piece of the eventual kingdom, and recruited a lot of interested parties. The mass rush of villains wore down the Avengers both physically and mentally, which allowed Kang to grab hold of Earth's defense systems.
Kang then used that power to destroy all of Washington D.C., which killed millions of men, women and children. Kang is eventually defeated, but the impact of his actions touched an untold amount of families. On one hand, it's not quite the death toll of an event by Infinity War, but let's also remember that those people came back. These people stayed dead, though I guess with a villain like Kang, that can change any time he travels backward in time.
Kang Raised Black Bolt’s Son To Destroy The Inhumans
When the modern Secret Wars event hit Marvel Comics, Black Bolt struck a deal with Kang The Conqueror in an attempt to spare his child Ahura from what led to it all. Kang agreed, but as all villains do, had a secret plan that resulted in him manipulating Ahura and turning him into another iteration of Kang The Conqueror who would ultimately go up against the Inhumans in the future.
Ultimately, the Inhumans were forced to kill the adult Ahura knowing full well who he was, but there is an upside. They were able to somehow save the young Ahura of the past, so the child ultimately survived. Even so, the fact that Kang would do something so wild and evil as to pit a child against their own parents later in life just shows what the unhinged villain is willing to do. He may be chill in his ultimately realized future self, but that's not the case in his earlier years.
Kang Eradicated An Entire Council Of Kangs
Yes, believe it or not, Rick and Morty is not the first science fiction series to imagine a bunch of multiversal variants banding together to make their own council. Kang also had the same thing happen to him, though these Kangs were folks who killed the Kangs of their universe or timelines and took over his role. They were all out in search of the Celestial Madonna, which put them up against the OG Kang.
The Kangs went to battle the original Kang, and as one would expect, the original came out on top. In fact, he managed to defeat all of them in Limbo when he harnessed the power of Alioth, that weird smoke beast Marvel fans may remember from Loki. Unfortunately, it doesn't seem like those others Kangs also had an Alioth, or they may have had a better shot at overcoming that.
Kang Tried To Kill All The Mutants
One thing Marvel fans will learn about Kang is that sometimes he spots moments in history that interfere with his long-term plans down the road, and interjects in an attempt to better his status in the future. This is one of those times, as Kang saw his plans as future ruler thwarted by the then-leaders of the mutants, Eimen and Uriel. The twins are the sons of "the final Horsemen" of Apocalypse, Ichisumi and Archangel, and a formidable duo that, you guessed it, were abducted by Kang as children. There's a real theme to Kang's plots we should really address at some point.
Unlike with Black Bolt's child, Uriel and Eimen rebelled and looked to thwart their adoptive father's plans. Of course, Kang saw this coming and their rebellion actually nearly resulted in all of mutantkind being wiped out, which would've changed the entire Marvel universe as we knew it. Of course, that's exactly why it couldn't happen... though could that be why we haven't seen mutants in the MCU yet?
Kang Tried To Make Spider-Punk A Sell-Out
To close things out on a lighter, but still despicable note, Kang once tried to make Spider-Punk (the punk rock multiversal version of Spider-Man) a sell-out. Under the alias of Kang The Conglomerator, he arrived from the future to let the hero know that he'd acquired the full licensing rights to Hobie Brown, the secret identity of Spider-Punk. Essentially, he owned the rights to the hero and wanted to market the hero to the fullest extent.
Obviously, there's nothing worse for anyone in punk rock than selling out. Spider-Punk was successfully able to thwart Kang The Conglomerator and avoid that fate. Kang was defeated, but threw in the final jab that Spider-Punk would die at a young age. That's probably the worst thing to hear from someone from the future, and no doubt the meanest thing they could say.