Blood Wolf Leader

A Pup is a wolf-like creature found on the 28th Floor of Aincrad Castle.

Sword Art Online
Klein and his guild Fuurinkazan where battling a group of Pups in the Wolf Plains after the lead group have cleared the 28th floor. It is where Kirito and Klein met up again for the first time, since they last saw each other in the Starting City and parted after the death game introduction.