Gozu (Root)

was a member of Konohagakure's Root, a faction of the Anbu led by Danzō Shimura.

Background
Gozu and his older twin brother, Mezu, were surgically altered to look like Kagen Uchiha, allowing them to take turns spying on the Uchiha clan by impersonating Kagen. Both reported directly to Danzō about their findings for several years, but in the year leading up to the Uchiha Clan Downfall they also helped Itachi Uchiha as he tried to avert the clan's attempted coup. After the clan was wiped out, Gozu was apparently killed by Itachi so that Itachi could impersonate him and get close to Danzō.