Gamaken

is a giant toad that was first summoned by Jiraiya during his battle against Pain.

Appearance
Gamaken is a giant magenta toad with black markings on his face, arms, and legs with horn like protrusions on his head, he was nearly as big as Gamabunta, and could tower over most buildings (except for the massive skyscrapers in Amegakure which dwarfed even other summons), trees and large rock formations. He wears a robe similar to Gamabunta's and keeps a sakazuki-like shield wrapped around his back and a sasumata in his hand.

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 ungraceful he is to Gamabunta. Despite this, he has shown no signs of being anymore clumsy or "ungraceful" 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.

Abilities
Gamaken is a strong toad who prefers fighting with taijutsu. He wields both a sasumata-like weapon and a shield. He is a skilled fighter, being able to fend off many different summons while Jiraiya prepared to summon the toad elders. In the anime he could use his sasumata to create various explosions. He was also very agile as he evaded many attacks while fighting in an industrialized city. He has great endurance and commitment to Jiraiya as he had taken many bite wounds from Pain's dog summon and still continued to fight.

Hunt for Itachi 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. They combatted the various animals summoned by the Animal Path until they were sent flying beyond Konoha's borders by the Deva Path.

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.