Hagoromo Ōtsutsuki

The was said to be the legendary figure who founded the ninja way and was the first to invent ninjutsu. He was said to be the only shinobi to possess the Rinnegan, which presumably laid the groundwork for the other dōjutsu, the Sharingan and the Byakugan.

As of now, the only other person to be known to possess the Rinnegan is Akatsuki's Pain. He is revered as the most legendary being in the naruto universe also is one of if not the strongest ninja in the naruto world. Whether this means that the Rinnegan is a unique Kekkei Genkai, that isn't passed down by blood, or if Pain is directly related to the Sage of the Six Paths is currently a mystery.