Guruko

is a ninken and a personal summon of Kakashi Hatake.

Background
In the anime, some time after Guroko and the other ninken made a contract with Kakashi, they aided him search 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 dogs. 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.

Land of Waves Arc
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 Retrieval Arc
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.

Ultimate Weapon Arc
He along with the other ninken were summoned by Kakashi to investigate the Takumi Village.

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