For almost a decade now, the titan Thanos was the ultimate bad guy driving conflict in the Marvel Cinematic Universe. As one of the most iconic and powerful antagonists in Marvel's supervillain roster, Thanos was an excellent choice to oppose the Avengers on the big screen. But with Thanos defeated, many are now speculating that the next major villain in the MCU could be Jonathan Majors as Kang the Conqueror. This would be an interesting direction for the franchise, as Kang is a very different kind of villain from Thanos. For starters, he's actually beaten the Avengers, fair and square.
Kang the Conqueror is a time-travelling warlord from the future who's obsessed with finding worthy opponents to battle throughout space and time. Naturally this obsession has drawn him to the modern age of superheroes and Kang considers the Avengers to be the ultimate opponent for him to overcome. But what's so special about Kang is that he doesn't just want to erase Earth's Mightiest Heroes - that would be unsportsmanlike. Kang wants to defeat the Avengers in open combat and conquer the earth with his superior tactics, not with cheap tricks. And in 2001, to the surprise of everyone on Earth, he did just that.
The Kang Dynasty (Or Kang War) is the name of the 16 issue Avengers storyline by writer Kurt Busiek and artist Alan Davis. The story is notable not just for its length (Busiek, a master of continuity, used the story to tie together multiple other plot lines from his Avengers run), but for being the only time in Mainstream continuity that the Avengers lost to a villain so completely that the entire Earth was forced to surrender. Kang War begins with Kang returning to Earth alongside his newly introduced son, Marcus, with Kang telling the Avengers that they must give up now or face the full wrath of his futuristic army. Naturally the Avengers say no - they've beaten villains like Kang before, so why would this time be any different?
Unfortunately for the heroes, the Conqueror isn't playing around this time. Using his time travel technology Kang unleashes his armies all over the world in coordinated attacks, and the Avengers become so overwhelmed by enemies they're left with no choice but to stand down to prevent further casualties. This all culminates in Avengers #49 where the entire planet formally surrenders to Kang's forces- and just to rub salt in the wound, he insists that the Avengers be the ones to sign the Declaration of Surrender.
For the first time ever, the Avengers have been beaten by a supervillain on every level. The heroes of earth weren't going to take this defeat lying down however - after all, they're the Avengers, so now it was time to avenge the planet. Interestingly the overthrow of Kang's new world order would actually be caused by one of his own allies, Marcus. Kang had spent years grooming the boy to be his perfect successor yet during the battle with the Avengers Marcus ended up developing an attraction to Warbird, one of Carol Danvers' many past hero identities. With help from Marcus, the Avengers are able to subvert Kang's regime from within and launch a counter offensive, culminating in a one-on-one showdown between Captain America and Kang.
What's especially good about this fight is the contrasting mentalities between the fighters. Kang is full of hubris and considers it an honor to fight the legendary Captain America, while Steve Rogers plainly tells him that there is no honor in war and that he's brought nothing but death to the world. After this final defeat, Kang resigns himself to be executed for his crimes, satisfied knowing that he achieved his dream and beat the Avengers on his terms - that is until he realizes Marcus is the one who cost him his victory. Kang once again dons his battle Armor and kills Marcus before returning to the future to plot his next conquest. Because while he can tolerate defeat at the hands of a worthy opponent the one thing Kang the Conqueror will never accept is a traitor to his empire.