Guruko

is a ninken and a personal summon of Kakashi Hatake.

Background
In the anime, after they made a contract with Kakashi, Guruko and the other ninken aided him to search the abducted Rin Nohara by the Kirigakure shinobi and acted as a diversion in order to allow them to flee. They also helped searching for the fleeing Orochimaru.

Appearance
He has tan fur, a white snout, long ears that have a dark brown colour and noticeably more pronounced whiskers than the other ninken. He wears the standard outfit of Kakashi's ninken, which consists of a blue vest with the heno-heno-moheji seal and a Konoha forehead protector on his forehead.

Abilities
Guruko possesses heightened senses with which he can use to track his target with ease. He has also demonstrated the ability to track his target underground through the use of the Summoning: Earth Release: Tracking Fang Technique as well as hold a target down, allowing Kakashi to attack them freely. He also has has exceptional teamwork with the rest of his pack, able to develop and effectively use several offensive and defensive formations in battle which make use of the manoeuvrability and powerful limbs.

Prologue — Land of Waves
Kakashi called on Guruko and the ninken pack to track and capture the missing-nin Zabuza Momochi. They managed to bite onto the missing-nin and pin him in place. This allowed Kakashi to use Lightning Cutter without fear of a counter attack.

Sasuke Recovery Mission
Later, Guruko and his fellow ninken were summoned by Kakashi to track down Naruto Uzumaki and his team who had gone off in pursuit of Sasuke Uchiha.

Sunagakure Support Mission
He along with the other ninken were summoned by Kakashi to investigate the Takumi Village.

Kazekage Rescue Mission
At the start of Part II, Guruko and the ninken pack were called upon to track down the Akatsuki member Sasori using a small piece of his clothing.

Itachi Pursuit Mission
Some weeks later, Kakashi summoned the pack to help track down Itachi Uchiha. He and Akino partnered with Shino.

Kakashi Hiden: Lightning in the Icy Sky
Kakashi summons Guruko and the other ninken to search for the exploding tags planted around the Tobishachimaru. Once they gather all the tags, the ninken give them to Might Guy.