Warning! Spoilers ahead for Kang the Conqueror #1
In Marvel Comics' new Kang the Conqueror series, the time-traveling villain meets his downfall with the reveal that his greatest enemy is himself. Choosing to conquer himself in this new series, Kang recruits his younger, teenaged self, back when he still went by Nathaniel Richards. Using his years and vast knowledge of time and the multiverse, Kang begins training Nathaniel, though this eventually leads to the Marvel villain's doom by the issue's end.
In Kang the Conqueror #1 from writers Collin Kelly and Jackson Lanzing with artist Carlos Magno, Kang travels back through his personal timeline to meet with Nathaniel (who had yet to conquer anything while growing up in the 31st century). Offering himself as Nathaniel's guide and mentor, Kang began training the young man, showing him the scope of his life and conquest as a time-traveling despot, while also showing him his failures and mistakes so that he might learn from them as well. However, it seems as though Kang's goal of creating a superior conqueror worked too well.
Eventually, Nathaniel realizes that there are some failures and vulnerabilities that even Kang hasn't been able to conquer within himself, which leads Nathaniel to believe Kang to be his inferior. For example, when Nathaniel finds love and starts thinking about being a hero (like when he became Iron Lad), Kang shuts him down and slaughters the village and girl Nathaniel had formed a connection with. This pushed Nathaniel over the edge, prompting him to steal Kang's suit and equipment for himself, leaving Kang to die from a prehistoric meteor. Apparently, Kang's ultimate demise was creating a superior version of himself who became his greatest enemy.
Rather than becoming a hero, this Nathaniel has now become darker and vengeful with a broken heart, succeeding his older self to become a superior conqueror determined to grow beyond the mistakes and weaknesses of the preceding Kang. However, the suit only had enough power for one jump, taking him from Kang's training in the Cretaceous period to the age of Rama-Tut (Kang's alias when he was a ruler of Egypt). Clearly, Nathaniel has yet to escape the metaphorical cage created by future versions of himself, and it looks as though there will still be much to learn from Rama-Tut's Kang.
In any case, there's some strong poetic justice that comes from Kang's doom being his attempt to improve himself. His great flaw was focusing his efforts outward to a younger version of himself rather than directly inward on a personal level. That mistake is what created the superior Kang who eventually rejected him and became his greatest enemy. Now, a new Kang the Conqueror has been born and it's going to be really interesting to see where his travels through time take him next with Rama-Tut and beyond.