Yonnin

"So, we all have met on the field of battle once more...Echo, Hikaru, and you...Seireitou." "Hmph... so it's come down to this? Feh.." "To think you would fall so far...so this is the taint of the Uchiha.." "Ryun... you may have crossed the line... but you're still our comrade, see the light already!" "The light you and I see are different. From this day forward, we are the Legendary Four no longer...!"

- Ryun Uchiha, Hikaru "Shadow" Kurosaki, Echo Osore, and Seireitou Kawahiru

The Legendary Four (伝説の四忍, Dendetsu no Yon; literally "legendary four ninja"), or known as the Yonnin (四忍者, Four Ninja), are the four strongest shinobi to have ever come forth as the successors to the Sage of Six Paths. Regarded in modern legend as both heros and villains, their names were made known far and wide. They possess exemplary ninja abilities. The Yonnin are widely regarded for their great skill and power, each one effortlessly succeeding a Kage's strength in their own right. Following the death of Seireitou Kawahiru, the Yonnin were disbanded, though they continued to be known by the title.

Renown
Seireitou Kawahiru: Known as Silver-Haired Seireitou, as well as the most arrogant of the four shinobi, Seireitou was the only one of the four to have died. In the fight battle against his older brother, in an effort to save his friend, he used the Kawahiru forbidden jutsu which ended up killing himself and Kamui in a single instant. From that point on, the Yonnin were officially disbanded.

Ryun Uchiha: Known as Tsukiakari no Michishirube, Ryun was the most emotional of the four, but also one of the strongest and honest. However, in the original formation of the four, Ryun considered himself the weakest of the four in terms of brute strength, but made up for it with ingenius tactics. He currently takes up residence within Iwagakure, and serves as one of their strongest warriors.

Hikaru "Shadow" Kurosaki: Known as Hikaru of the Shadows, Hikaru was considered the eldest of the group and the wisest member. In the original formation, Hikaru was no doubt the strongest and most intelligent of the four, with Seireitou constantly attempting to surpass him. It is unknown where Hikaru currently resides, but it is rumored that he retired from battle, and self-exiled himself to the Lost Lands.

Echo Osore: Once known as Echo of the Demonic Sharingan, Echo was the "bad boy" of the four, and served as Ryun's main partner in the past. He was feared for his usage of a green mutated Sharingan, as well as the demonic powers he held. Since then, he has mysteriously went through changes, and it is currently unknown where he resides, if still alive.

Behind the Scenes
These four were once given the name Yonkō, but it was replaced with the term Yonnin. The Yonnin also is the term that denotes the strong friendship between the four users of the Yonnin's four ninjas: Seireitou, Tenny, Kuro-san, and Echo. Since back then, only two are currently active on a consistent basis, Seireitou and Ten.