Gamaken

is a giant toad that was summoned by Jiraiya during his fight with Pain. He wields a sasumata-like weapon and a shield. He also seems to be wearing the same robe as Gamabunta.

Personality
He is constantly referring to how clumsy he is, and constantly seems nervous, albeit he also says he will do his best. Like most other toads he has no real respect for Jiraiya, and when scolded about ruining Jiraiyas pose, he just responded by saying that it is not his fault, but Jiraiya's fault for being klutzier than a drunken monkey.

Despite being "clumsy" and his lack of respect for Jiraiya, he seems to be a skilled fighter while fighting alongside Naruto

Infiltration of Amagekure
He was first summoned by Jiraiya, when he was facing the Akatsuki leader Pain, and decided to use the Hermit Mode. However in order to use Hermit 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 various animal summons and was kicked back and forth throughout the tower they were in, until he was pushed into a sewer where Jiraiya told him to return as he was finally finished.

Invasion of Pain
He was later summoned again by Shima right after Pain destroyed most of Konoha. He, along with the Gamabunta and Gamahiro, fought against three of Pain's summons with Gamaken taking on the giant rhino that Pain summons, swatting him away with his weapon.

Abilities
Not much is known about his abilities, only that he is a sturdy fighter with a great deal of defensive capabilities, and that he seems well versed in using his shield and staff weapon, while still being able to protect a human standing on his head.