Sharingan

The Sharingan, literally "Copy Wheel Eye", is the inherited eye ability of the Uchiha clan. It lets its user see through illusions and pick up otherwise imperceptible movements at a superhuman rate, and it manifests when a clan member goes through deep emotional trauma.

Lore & Background

Kakashi Hatake carries a Sharingan he received from his teammate Obito Uchiha; it lets him mimic the movements and jutsu of others, and he is revered as the ninja who has copied over a thousand techniques. The eye can advance to the Mangekyo Sharingan, as Sasuke's does after his brother's death.

Reader's Guide

Overuse of the Mangekyo Sharingan blinded Madara Uchiha, who took the eyes of his late brother Izuna and gained the Eternal Mangekyo Sharingan. Sasuke later has Itachi's eyes implanted in the same way. Masashi Kishimoto has said the ability was influenced by the character Hiei from YuYu Hakusho.