Many popular works of fiction depict characters who are really two people in one, and they often use the classic Dr. Jekyll and Mr. Hyde story as an example. The popular animated series Naruto did this with its minor villain/antihero Jugo, who was once a test subject of the cruel rogue scientist Orochimaru. He's no ordinary ninja.
Jugo is the progenitor of the terrifying but powerful curse seal technique, and he is also known for "Hulking out" in fits of violent, uncontrollable rage. That, combined with the gentle nature of his true personality, makes him the Bruce Banner of Naruto, and it perfectly explains how the curse seal came to be.
How Jugo Became Naruto's Hulk
Little is known of Jugo's birthplace or childhood except for key details about his fits of rage and the woes it brought. Jugo was ordinarily a mild-mannered boy, but anything could provoke him into sudden bouts of extreme anger and violence, making him a pariah and a monster in the eyes of his fellow villagers. Eventually, Jugo was banished to a cave where he couldn't harm anyone else, and he was effectively abandoned. There, Jugo was met by Kaguya Kimimaro, the bearer of a bone-based kekkei genkai, who befriended him. This led Jugo to meet Orochimaru, and Jugo volunteered as a test subject.
Orochimaru had failed to fully learn Sage Mode, or senjutsu, so instead, he combined sage chakra with Jugo's blood enzymes in a brilliant experiment to create something entirely new. The curse seal was born, and Jugo was its first-ever bearer. This particular jutsu allowed the wielder to manually enter stage one, which covers the skin with dark patterns, and stage two, which mutates the body into something monstrous.
Notably, Jugo can morph his body into a variety of forms while absorbing natural energy, while other curse mark bearers, such as the Sound Four's members and Uchiha Sasuke, can only assume one particular form. Jugo enters a berserker rage when he fully transforms, and even his voice changes into something more monstrous. However, Jugo does not identify very strongly with any of this, and he doesn't derive much pride from it. In fact, he seems to resent his very nature. This makes him more akin to the MCU's Bruce Banner than true sadists like Sasori and Kisame.
How Jugo & Bruce Banner Manage Their Dual Natures
Both Jugo and Bruce Banner struggle to reconcile their opposing halves, but they have found helpful ways to manage their dual natures, and this can be inspiring for fans of Naruto, the MCU or both. Jugo has practiced self-isolation more than once, based on his experience of being exiled from his village, and he fears not loneliness but harming others. Jugo is a selfless being, preferring to spend his time in nature rather than around other people, a bit like Koda Koji from My Hero Academia. This is his Bruce Banner half, a pacifistic young man who bears the serious burden of being a monster on the inside.
This weighs heavily on him, but he found solace when he was recruited by Sasuke, who had methods for keeping his rampages in check. Jugo has come to appreciate his new friends, and he fights hard for their sake. At last, he has channeled his unstoppable rage and strength into something more productive, which makes him more of an antihero than Sasuke, Karin or Suigetsu.
Similarly, Bruce Banner used to bitterly hate his Hulk half, and as he put it in The Avengers, he "got low" and tried to end it all. He failed and decided to put himself to work helping others, both as Bruce the scientist and the incredible Hulk, a powerful Avenger. Like Jugo, Bruce works better in a team where everyone can keep him in check, and both characters can trust other people to restrain them because they cannot predict or restrain themselves.
In that way, both Jugo and Bruce Banner represent the power of friendship and how it can not only create bonds between two people, but also reshape and even "cure" them to a degree. Jugo and Bruce never got anything done hiding out of shame and fear -- they took responsibility for their wild strength and joined a team with trustworthy friends, and that could speak to many fans on a deep level. Jugo's and Bruce's struggles may be resonant to fans and make them more sympathetic and even inspiring, and prove that no one is truly a monster, even if they think they are. There's always more than one side to a person, and they should not be condemned for their worst side. They have so much more to give.
