Gamahiro

Other then his name, not much is known about. He's comparable in size to Gamabunta and likely one of the most powerful toads, since he was summoned together with Gamabunta, Gamaken, and Gamakichi to fight against Pain.

Konoha Invasion Arc
He first appeared in the Konoha Invasion Arc when Jiraiya used him to fight Orochimaru's large snakes by using Summoning: Food Cart Destroyer Technique.

Post Sasuke Retrieval Arc
He was summoned by Jiraiya to help Sasame Fuma, Sakura Haruno, and Naruto Uzumaki get out of Orochimaru's hideout.

Invasion of Pain
He was again summoned, this time by Shima during Pain's invasion of Konoha. He was then ordered to kill a summon by Naruto.

After Deva Pain regained his powers, Gamahiro and the other toads tried to kill him but Pain sent them flying with a Shinra Tensa attack. He is currently laying motionless under a lake.

Abilties
He is comparable in size to Gamabunta which could indicate that he is very powerful.

Trivia

 * He has different skin color between the anime, where he has a green and brown theme, and the manga; where he has a bluish theme. This is most likely due to him being coloured in the anime before the manga.