Gamaken

is a giant toad that resides on Mount Myōboku. He is sometimes referred to simply as "Ken".

Personality
Gamaken is very modest. He is constantly referring to how clumsy he is, and often seems nervous. While fighting the Animal Path's summons during Pain's invasion, he once again states how clumsy he is to Gamabunta. Despite this, he has shown no signs of being any more clumsy or "clumsy" than other toads in the series, albeit he also says that he will always do his best. His nickname "Ken-san" gives him a sense of reliability like that of someone who will definitely be there for a timely rescue when in dire straits.

Appearance
Gamaken is a giant magenta toad with black markings on his face, arms, and legs with horn like protrusions on his head. He is as big as Gamabunta, and towers over most buildings (except for the massive skyscrapers in Amegakure which dwarfed even other summons), trees and large rock formations. He wears a black kimono with a white sash and mesh armour underneath. He keeps a sakazuki-like shield wrapped around his back and his sasumata in his hand.

Abilities
In spite of his lack of confidence in his abilities, Gamaken is actually a very powerful combatant. His fighting style revolved around armed melee combat with both a sasumata and a sakazuki shield which he wields with extreme proficiency. His skill was shown both times he confronted Pain's summons as he was initially able to fend off many different summons while Jiraiya prepared to summon the Two Great Sage Toads and then later able to deal a detrimental blow to Pain's Giant Rhino when summoned to defend Konoha. In the anime his satsumata can be used to create explosions adding an even more deadly surprise to his attacks. He is also very agile as he evaded many attacks while fighting in an industrialised city. He uses his shield both defensively, to guard against attacks as well as like a flail and even for other supplementary purposes. He has great endurance and commitment as he had taken many bite wounds from Pain's dog summon but nevertheless, still continued to fight.

Itachi Pursuit Arc
He was first summoned by Jiraiya when he was facing the Akatsuki leader Pain and decided to use the Sage Mode. However, in order to use Sage Mode, it would take him some time to prepare it, and he could not afford to take the risk of leaving himself unprotected, so he summoned Gamaken. During the time it took for Jiraiya to prepare the technique, Gamaken was forced to face off with a great variety of Pain's animal summons, and was kicked back and forth throughout the tower they were in until he was pushed into a sewer, after which Jiraiya then told him to return as he had finally finished the preparation for his technique.

Invasion of Pain Arc
Gamaken, along with Gamabunta and Gamahiro, were later summoned to assist in Naruto's fight with Pain. He directly confronts the Giant Rhino summoned by the Animal Path attacking it with his sasumata, damaging it extensively. He later engages Pain's Giant Multi-Headed Dog once again and warns Gamabunta and Gamahiro of its ability albeit a little too late according to Gamabunta. After Naruto incapacitates the Animal Path and the summons disappear, the toads confront the Preta and Deva Path until the latter sends them flying beyond Konoha's borders with Shinra Tensei. He was later seen passed out after crashing into some mountains.

Trivia

 * Though likely unofficial, it was revealed in the post-credits omake of Naruto Shippūden episode 164 that he operates a tavern in Mount Myōboku, where other giant toads like Gamabunta and even Katsuyu frequently hang out.
 * Gamaken's name comes from the well-known Yakuza actor who is seen as somewhat of a rival to Bunta Sugawara: Ken Takakura.

Quotes

 * (To Jiraiya) "Though I'm pretty weak, I'll try my best."
 * "I guess I really am… just… clumsy."