Pakkun

is a petite pug and the smallest of Kakashi Hatake's Ninken. Pakkun is seemingly the most intelligent of the ninken, and has the ability to speak. Also in accordance to the anime, Pakkun was able to say Kakashi's name at four months of age. This implies that Kakashi's Ninken may have been all raised from a young age by him. Despite his cute appearance, his voice is deep and gruff. When Pakkun, Naruto, and Sakura appear to help Sasuke in the battle against Gaara, he reveals that he is not a battle type ninja dog, which Sakura claims to know by looking at his small appearance. In the anime, he reveals that he uses Floral Green shampoo (Minty Rain forest Mist Shampoo with extra body in the English dub), which is also used by Sakura Haruno (Sakura is comically traumatized at the thought of using the same shampoo as a dog).

Journey to the Land of Waves arc
Pakkun makes his first appearance as a small cameo with the rest of the Kakashi's ninken. When Kakashi decides he has to finish his battle against Zabuza quickly to reseal Naruto's demon chakra, he performs his Summoning Technique: Earth Release: Tracking Fang Technique. Pakkun, along with the other ninken, use their sense of smell to track Zabuza using Kakashi's blood that is on Zabuza's blade. He is seen hanging off Zabuza's headband. As they pin Zabuza down, Kakashi goes in for the kill with his Lightning Blade, only to be intercepted by Haku.

Invasion of Konoha
During the attack on Konoha, Kakashi is unable to aid Sasuke in his pursuit of Gaara. Instead, he orders Naruto, Sakura, and Shikamaru to help Sasuke. To aid them in finding Sasuke, Kakashi summons Pakkun, who makes his first speaking appearance. Sakura is shocked to see a rationally thinking and talking dog. Shikamaru refuses to help in finding Sasuke, and Pakkun tells him if he completes this mission he will let him touch the pads on his feet. He claims they are really soft and supple. When Pakkun, Naruto, and Sakura appear to help Sasuke in the battle against Gaara, he reveals that he is not a battle type ninja dog, which Sakura claims to know by looking at his small appearance.

Sasuke Retrieval arc
When Kakashi learns about Sasuke's defection and that a team was formed to retrieve him, Kakashi decides to go after them, effectively ignoring his orders to go on a S-rank mission. Pakkun is summoned with the rest of the ninken to find their trail. After they find an unconscious Naruto, Pakkun regretfully tells Kakashi the rain as washed away Sasuke's scent and any chance of following him.

Pre-Shippūden filler arc
Pakkun made a few appearances during the anime filler arcs leading up to Shippūden. His first appearance was during Mizuki's escape from prison when Kakashi summoned Pakkun to aid Iruka in recapturing Mizuki (at this point Kakashi comically summoned Pakkun directly into Iruka's hand). Pakkun's next appearance was during the mission to the Land of Birds where he helped Kakashi find a ninja that was camouflaging himself. Pakkun had a very comedic scene where he bit the ninja's hand and another scene where he broke his fangs on the ninja's jutsu-enduced rock body. His last appearance was during the last filler arc where he and the rest of the ninken went to investigate the rumors about the Takumi Village's uprising.

Rescue Gaara arc
After Team Kakashi learns about Gaara's capture by the Akatsuki, Kakashi summons the ninken again to find their trail. After find the enemy's lair and reporting to Kakashi, Pakkun is sent to find Team Guy and lead them to the enemy. When Team Guy faces against Kisame Pakkun becomes angry that he cannot help them as he knows he would just be a burden to the team.

Three-Tails Arrival filler arc
When Kakashi and his team find several victims of a unique crystal jutsu, Kakashi summons Pakkun and has him take one of Shino's insects that was trapped in one of crystals back to Tsunade for analysis.

Hunt for Uchiha arc
After it is decided to hunt for Itachi Uchiha in hopes it would help in their search for Sasuke, Pakkun and the rest of the ninken are summoned to find the trail.

Abilities
Despite his small size, Pakkun has shown to be a very useful summon. Pakkun has repeatedly shown to have an incredibly sharp sense of smell even by canine standards. He can regularly determine what type of scent he is picking up, how far it is, and how dangerous he is. Also, he has shown to have tremendous speed from how effectively he can keep up with full-grown human ninjas.

Trivia

 * During the invasion of Konoha, Pakkun's offer to Shikamaru to touch his pads is a reference to modern Japanese culture, in which a dog's paw is considered its cutest aspect; the idea of an animal's paw being "cute," however, applies mainly to puppies and kittens, because at birth their pads are pink, and as dogs grow older, they turn into a dirty black.
 * Pakkun is one of few summonings that is seen wearing a shinobi village emblem.