F

is a Kumogakure shinobi.

Appearance
F has short spiky hair, a well-defined nose, a small goatee and wore the standard uniform of Kumogakure shinobi along with the forehead protector.

Shinobi World War Arc
During the Fourth Shinobi World War, F was attacked by a White Zetsu clone on the battlefield and was later impersonated by this clone. It is unknown if the real F is still alive.

Trivia

 * His name is the Japanese pronunciation of the English letter "F". This is similar to the names of A, Killer B, C, and J, that are the pronunciations of the letters "A", "B", "C", and "J", respectively.