While Jugo’s clan gained incredible strength, the raw nature energy often drove them into uncontrollable rages. Orochimaru isolated the enzyme responsible for these transformations and combined it with his own to create the Curse Seal. By branding others with this seal, he could grant them a pseudo-Sage Mode without the years of rigorous training required to master actual Senjutsu. How the Seal Functions
Here is a comprehensive guide to the Cursed Seal, covering its origins, mechanics, levels of power, and known users. naruto curse seal