Akamaru

is Kiba Inuzuka's, along with his best friend and companion.

Background
At some point, while Kiba was still in the academy, his mother, Tsume Inuzuka, entrusted him with Akamaru. Although Akamaru almost immediately urinated on Kiba's face, much to Tsume and Hana Inuzuka's amusement, the two became close.

Chunin Exam arc
Akamaru helped Kiba cheat in the first test, sitting on his head to keep an eye out for proctors and to get information from other exam takers. On their way to the tower during the second test, Kiba had the group stop to investigate Gaara's encounter with Team Shigure. Akamaru was immediately frightened by sensing the strength of Gaara's chakra, and was traumatized by seeing Gaara brutally kill all three Rain Genin.

Akamaru fought alongside Kiba against Naruto Uzumaki in the exam preliminaries. He was considered a ninja tool rather than an additional combatant, and was thus permitted to fight alongside Kiba. While Akamaru gave Naruto some difficulty, especially after he transformed into a clone of Kiba, Naruto was able to use Akamaru to trick Kiba, first transforming into Akamaru and coming out of the smoke bomb to ambush him. After Kiba used the Beast Human Clone technique, Naruto turned into Kiba to prevent Kiba from attacking him, and when Kiba saw through his plan, transformed into Akamaru to make him think that he had hit Akamaru. Kiba then punched Akamaru, believing him to be Naruto.

In the finals, Akamaru was knocked out along with Kiba after Kabuto Yakushi, disguised as an ANBU member, healed Hinata Hyuga. In the anime, Akamaru attempted to warn Kiba about Kabuto, possibly having recognized who he was.

Sasuke Retrieval arc
Over time, Kiba and Akamaru developed Dynamic Marking and Double Wolf Fang together. In the mission to retrieve Sasuke, Kiba and Akamaru remained with the group until they retrieved the container, but an exploding tag blew them and Sakon and Ukon into a canyon. Kiba and Akamaru initially struggled against the brothers, and Akamaru realized that they must use Double Wolf Fang. Kiba was hesitant, given the large amount of chakra needed, which would render them vulnerable if they missed. Akamaru bit him on the hand, and Kiba, realizing that Akamaru saw him as pathetic, decided to take the risk. The attack severely wounded Sakon and Ukon, but they blocked the last attack with a Rashomon barrier, and Akamaru was injured protecting Kiba from their counterattack, but managed to urinate in Sakon's eyes at the same time. When Ukon began taking over Kiba's body, he stabbed himself in the chest in an attempt to kill Sakon to prevent himself from being taken over and harming Akamaru. Kiba attempted to escape with Akamaru, and, after Sakon and Ukon caught up with them, Kankuro arrived and killed both of them.

Kiba and Akamaru's injuries took some time to heal. Kiba, not wanting Akamaru to suffer that much again, vowed to improve himself.

Filler arcs
Akamaru accompanied Kiba on his missions with Naruto in the fillers. In the Treasure Hunt arc, his presence was used as Kiba's proof of being the real Kiba, as, while his impostor could imitate his face, he could not replace Akamaru.

In Episode 184, Akamaru was infected with a toxin that caused him to go berserk. When he attacked some ANBU members who were training, the order was given to have him taken into custody. As Hana attempted to make a cure for Akamaru, Kiba smuggled his dog out of the village and escaped, having heard that Akamaru might need to be killed, but Akamaru continued to lose control of himself. By the time Naruto and Hana caught up with Kiba, Akamaru had turned into a giant version of himself, and attacked anyone near him. Kiba hesitated in the face of the possibility that Akamaru might die, but, after Naruto and Hana's attempt to pin Akamaru down and administer the antidote failed, Kiba apologized to Akamaru while standing still as Akamaru leapt at him. Kiba was severely injured, but managed to inject Akamaru with the antidote, and noted that Akamaru had tried his best to avoid killing him.

Sai and Sasuke arc
When Naruto met Kiba while looking for teammates, he noticed that Akamaru was much larger, especially given that Kiba was now riding on him rather than having him sit on his head. Naruto asked Kiba to join his team for a mission, and even proposed having Akamaru go with him without Kiba, but Kiba refused the suggestion.

Fire Temple arc
When Team Yamato returned from the Fire Temple with a young monk named Sora, Sora quickly made it known that he didn't care what any living thing thought of him. He quickly got into a staring contest with Akamaru, to which Kiba became annoyed at. When Furido and his men attacked the Leaf Village, Akamaru demonstrated that his new size also helped considerably in battle, as he was able to take down several zombies without transforming.

Three-Tails Arrival arc
When Kakashi was ordered to investigate the latest whereabouts of Orochimaru, Team Kurenai was assigned to work with him due to their tracking skills. When they managed to find Orochimaru's hideout, they triggered a trap that destroyed the base. Fortunately, Akamaru's nose was able to find a way out in time. Later, Akamaru began to have trouble concentrating due to a high-frequency sound. It was through this that the team realized that they were being spied on by bats. When the enemy ambushed them and rendered their sense of smell helpless with a smokescreen, Akamaru convinced Kiba to try their beast-like taijutsu to blow away the smoke.

Soon, the team found themselves being attacked by Guren. There, Kiba and Akamaru again worked together to fight off her attacks. After sensing their enemy's new overwhelming might, Akamaru saved Kiba by digging into the ground and hiding them in a pit.

Hunt for Itachi arc
After it was decided that the best way to find Sasuke was to find Itachi Uchiha, Akamaru and Kiba later assisted Naruto in searching for either of the Uchiha brothers, but they were unable to reach Sasuke in time and returned home.

Invasion of Pain arc
When Pain invaded Konoha, Kiba and Akamaru joined Kiba's mother in fighting the Preta path. Later, during the aftermath of the struggle, he appeared with Kiba riding him to warn Naruto and Sakura that Danzo had been appointed as the Sixth Hokage and had just given the order permitting ninjas to dispose of Sasuke as a missing-nin.

Abilities
In Part I, Kiba carried Akamaru around on top of his head or inside his jacket. In Part II, Akamaru has grown large enough for Kiba to ride on his back, a difference Kiba failed to notice due to the amount of time they spend together. Akamaru's heightened senses, such as smell and hearing, along with Kiba's ability to communicate with him, make him a powerful ally for gathering and sharing information; he can also sense chakra with his nose, so he can judge an enemy's strength and warn Kiba if they are particularly powerful. In combat, Akamaru typically takes Kiba's form (albeit having a much more feral appearance) upon Kiba's use of Beast Human Clone, or combining with Kiba into a single entity in more desperate situations. Because Akamaru lacks his own chakra reserves, Kiba performs many of the jutsu that Akamaru takes part in, although Akamaru is able to contribute when it comes to physical attacks. Akamaru can also use Dynamic Marking by urinating on a target with great accuracy, allowing either Kiba or Akamaru to easily track the target by scent, particularly when fused together.

Trivia

 * Aka means red. -maru is a suffix for Japanese male names. The reason for his name was explained by Kiba when Akamaru's fur turned red after eating a Military Rations Pill.
 * Akamaru's breed is similar to a Great Pyrenees.
 * His favorite food is the special dog food Kiba makes.
 * Akamaru is not to be confused with Kakashi Hatake's nin-dogs. Akamaru is an Inuzuka dog and is not a summon.
 * In an omake segment that aired in Japan for New Year's, Kiba attempted to get Akamaru to talk, with little success. There are no indications that Akamaru even has the potential to speak.
 * Interestingly, Naruto was first published in a segment of Weekly Shonen Jump known as "Akamaru Jump".
 * Akamaru and Naruto have the same seiyū, Junko Takeuchi. However, they have separate English voice actors.