Gozu (Root)

was a member of Konohagakure's Anbu faction Root.

Background
Gozu and his younger twin brother, Mezu, were surgically altered to look like Kagen Uchiha, allowing them to take turns spying on the Uchiha clan by impersonating Kagen. When not in the village impersonating Kagen, Gozu wore a red marked mask resembling a monkey. 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.

Trivia

 * Gozu and Mezu share similar names with another set of twins in the series, Meizu and Gōzu.
 * Gozu and Mezu shared their ANBU mask design, a monkey. Despite the identical design, the colors were different; Gozu's mask was red, while Mezu's mask was blue.