Warning: SPOILERS ahead for Cobra Kai season 3.
Terry Silver and Mike Barnes in The Karate Kid 3, he sought brutal vengeance against Mr. Miyagi and Daniel-san. The plan once again ended in defeat and humiliation.
John Kreese returned once more in Cobra Kai. For a time, it seemed as though he might have truly changed — with his status as homeless (living in a men's shelter) garnering Johnny's sympathy. However, Kreese's old habits ultimately resurfaced. Having seized control of the dojo, he poisoned a new generation to embrace his uncompromising ways. Simultaneously, flashbacks shed light on Kreese's past and the true origin of the Cobra Kai dojo's "no mercy" mantra. Though the new details fleshed Kreese out and humanized him, they didn't serve to make him sympathetic or facilitate redemption. Instead, the flashbacks just demonstrated what made him the villain that he is and emphasized that he's actually a truly terrifying individual.
For decades, John Kreese was viewed as larger-than-life and, arguably, even a somewhat cartoonish villain. However, his flashbacks dove headlong into what fueled his particular logic and processes. Equally, those scenes demonstrated how his methods are rooted in some serious psychological issues, Early in the new episodes, it was revealed that he'd lost his mother to suicide. Meanwhile, later in Cobra Kai season 3, Young Kreese suffered another tragic loss when his girlfriend was involved in a fatal car accident. He was already fearless to the point that he was accused of having a death wish. Following that latter death, though, he truly became a man with absolutely nothing anchoring him to his previous humanity.
Kreese had been fighting his entire life and survival had always been second nature to him. Only after losing everything, however, was he able to finally cross the line his captain had pushed him towards. In a case of poetic irony, it was letting that same captain die that fully set Kreese's mentality in stone. It was that moment that sealed for him that there was no middle ground. Survival had to mean the absolute defeat (or death) of your enemy — be it in the dojo, on the streets, or in competition. Unlike The Karate Kid 2's Chozen, who'd turned himself around, that black and white distinction remained intact and nestled itself even deeper in Kreese's personality.
That mentality previously seemed over-the-top, given the context of the movies. By depicting the genesis of his mental scars, however, Kreese became a psychologically-troubled character on a much more conceivable level. Kreese's belief was further solidified in the immediate aftermath of saving Terry Silver's life — when Kreese was pulled into a brotherly hug and gifted a lifelong debt. One of the reasons Kreese signed up for the military was to be a hero. And, at that moment, he received his wish. With that gesture, Kreese gained a seeming reward for his newly-merciless attitude and the closest thing to warmth he could probably still feel.
Like everything else in the flashbacks, it added deeper and more visible context — this time to why he continuously went back to teaching. Kreese craves both the gratification of violence and the iration of those who look up to him. Almost like a serial killer, everything was about recreating that experience in Vietnam. He'd developed a need for that hero worship. That cycle of merciless victory followed by immense gratitude gave him renewed purpose and a way of justifying his deranged actions. It equally explained why he murderously lashed out whenever he was denied such grateful loyalty. It's all he has. It's what he's lived almost his whole life for. And he wouldn't let anything but death keep him from it. As such, even the more absurdist elements of Cobra Kai - like settling violent, law-breaking feuds with the All-Valley Karate Tournament rather than the police - are now grounded in some richly-explored characterizations.