The Origin of Sukuna "Jujutsu Kaisen", the Curse King of Sukuna
The origin of Sukuna in the Jujutsu Kaisen Anime is indeed very briefly told. The story of his past is only informed at a glance from all the facts that exist. However, there are several theories that discuss the origin of the sukuna although they are not fully "justified".
Sukuna is the King of all Curses in the Jujutsu Kaisen anime. He is able to kill the target without moving at all, this is shown when he slashes Mahito and inflicts a very serious wound. Sukuna is a form of "pleasure" and "displeasure" himself, it makes him always arrogant and arrogant.
Until now, Sukuna only cares about 2 things, namely the agreement with Yuji Itadori and the fight with Megumi. Yuji Itadori is the vessel for the Cursed King Sukuna, while Megumi has the power that is considered "Potential" by Sukuna. This power is Megumi's Strongest Skill that she managed to use using the 10 Shadow Skill.
The Origin of Sukuna
The origin of the King of the Curse of Sukuna is in ancient times that is more than 1000 years ago. At first Sukuna was an ordinary human who was born since the golden age of Jujutsu Magicians, all of that happened more than 1000 years ago.
In the golden age of the Jujutsu Magicians which was more than 1000 years ago, Sukuna had killed many jujutsu Magicians. So at that time Sukuna had succeeded in slaughtering all the jujutsu magicians who were in their golden age. Well then the magicians decided to work together with the aim of "Killing" Sukuna. Sukuna was defeated but he could not be "Destroyed" and the remaining 20 Fingers became Cursed Objects.
The Sukuna's Cursed Finger is spread all over the country. After Itadori ate one of the Sukuna's fingers, he automatically became a container for the Sukuna. Now with the existence of "Wadah", Sukuna has the possibility to fully rise and return to continue the massacre he did as in the past.
Well, the theory above is a bit of information that explains why Sukuna can become the "King" of the Curse. Although he was originally a "Human" but Sukuna had killed many Jujutsu Magicians. It is possible that Sukuna was dubbed the "King" of the Curse because of his ability to kill many Shamans/Witches. Then Sukuna is also the only character who knows the true meaning of "Curse".