Shisui Uchiha (うちはシスイ, Uchiha Shisui), renowned as "Shisui of the Body Flicker" (瞬身のシスイ, Shunshin no Shisui, English TV: Shisui the Teleporter) and Shisui of the Sharingan, is a shinobi of Konohagakure's Uchiha clan. He is known to others as the son of the legendary war hero Kagami Uchiha and was seen as a prodigy thus matching up to Itachi's skills as it is shown that he is also seen as the true definition of an Uchiha.
Background At the end of the Third Shinobi World War, Shisui witnessed his best friend die without being able to do anything to save him, consequently awakening the Mangekyō Sharingan. A year later, he met a 5 year old Itachi Uchiha, becoming best friends and forming a brother-like bond. When Itachi began to act oddly, Shisui was instructed by the Konoha Military Police Force to monitor Itachi because the younger Uchiha's position in Anbu was instrumental to the Uchiha's future status in Konoha. Unbeknownst to the clan, Shisui in reality sympathised with Itachi, not wanting the Uchiha to go to war with the village.