Name : Gamabunta
Affiliation : Konohagakure (Hidden Leaf)
Summoners : Fourth Hokage, Jiraiya, Uzumaki Naruto
Seiyu : Takeshi Watabe
Signature Ability : Giant Dosu, Suiton: Tepp¨dama (Water Release: Gunshot), Gama Dosuzan (Toad Sword Beheading), Konbi Henge (Combination Transformation) (with Uzumaki Naruto), Katon: Gamayu Endan (Fire Release: Toad Oil Flame Bullet) (with Jiraiya)
Gamabunta is the boss of the toads that are summoned. He is huge (about 100 meters high) and is summoned for battles with the biggest of enemies. can only summon him with his Kyuubi chakra (whereas at first with his own, he is only capable of summoning up tadpoles or some of Gamabunta's small children). Naruto first summoned him in the month long training session with when Jiraiya pushed him over a cliff in order to induce life-threatening fear in Naruto so that the Kyuubi chakra could come out.
Gamabunta is a grumpy and highly apathetic character. He doesn't like to take orders from anyone, unless the summoner is highly talented and earns his respect. Jiraiya and the Yondaime Hokage are few of those people whom he allows them to ride on top of his head without question (although Jiraiya admits that he can't completely control Gamabunta). He uses some Japanese words that only a yakuza gangster would use. Still, he is portrayed as an ultimately powerful and positive force.
When Naruto first summoned Gamabunta, the Toad Boss didn't believe a little kid like Naruto could summon him. Naruto, angry at this comment, claimed that, as the Gamabunta's summoner, he was the toad's master. This, in turn, made Gamabunta lose his patience with Naruto and he threatened to kill him. The angry Gamabunta scared Naruto into submission and, after Naruto apologized, Gamabunta accepted him as a subordinate. Gamabunta didn't believe that Naruto summoned him until he saw the contract scroll left behind by Jiraiya. It's not until then that Gamabunta is really impressed by Naruto, claiming that no-one has ridden on his head since the Yondaime. Gamabunta then takes Naruto, exhausted because of the summoning, to the hospital, leaving his footprint as a signature.
In the anime, Naruto demanded to be recognized as Gamabunta's master if he could ride the toad until sundown. Naruto showed his great resilient spirit and almost made it. Regardless, Gamabunta was impressed, and didn't need the contract scroll to believe that Naruto had summoned him.
In the next summoning, Naruto is almost killed by 's Sabaku Sousou (Imploding Sand Funeral) attack when he performs the Kuchiyose no Jutsu (Summoning Technique). Gaara is in his full form of Shukaku (although he has not gone to sleep yet). Gamabunta is his usual grumpy self, and shares a dialog with Naruto about the fact that he promised to have a subordinate/mentor relationship with him but only after sharing sake ceremony (which of course is 8 years away because Naruto isn't old enough to drink yet, and wouldn't be of any good use to Naruto here and now in the current battle), at which point Gamakichi tells his father that Gaara bullied him and that Naruto saved him. Gamabunta, who is fiercely protective of his kin, was very impressed with Naruto, and not only does he officially accept him as his subordinate, but he also tells Naruto he will show him all about "Jingi" which is another yakuza term describing a highly argumentative honor code (although it's portrayed as a completely positive thing in this anime).
In the next summoning, while harmed by 's poison, Jiraiya, after summoning Gamakichi, finally collects his chakra focus and brings out Gamabunta for battle against Orochimaru's snake, Manda. It indicates that Gamabunta hates Manda's guts and would love to just cut into him. He seems to have respect for Katsuyu, Tsunade's summon, as he rescued her from Manda.
His next summon was in the filler arc against Umibozu the Sea Boss during the Sea Country Filler Arc. He got angry at Naruto because he wasn't adaptable in saltwater and it would dry him out quickly. Despite being in saltwater, Gamabunta fights anyway because he is underestimated by his opponent, which really annoys him.
Overall, despite his grumpy exterior, he shows respect towards Naruto as if he were a son. He even explained to Jiraiya that he's aware of Naruto's talents. There's indication that despite Jiraiya having trouble controlling him, they seem to be good friends and, as implied in the series, drinking buddies. However, on occasion he will scold him.