Gerotora

is a toad that watches over the scroll which acts as the "key" to the Eight Trigrams Seal on Naruto's stomach. Jiraiya eventually left the scroll to Naruto, so that he can learn the key jutsu.

Background
Gerotora writes seals and sealing formulas on his own abdomen, then he is "stored" inside the body of the contractor who affixed his seal on it and he closely guards the secret information until said contractor dies. Gerotora is one of the "scroll toads", a renowned species that is rare even in Myobokuzan. He is known to be especially secretive and to possess excellent endurance even among his kin. When the Nine-Tailed Demon Fox attacked Konoha, he was requested by the Fourth Hokage to protect the key to the "Eight Trigrams Seal" performed on Naruto's stomach, a heavy responsibility. He is still strictly adhering to the contract.

Infiltration of Amegakure
He first appears when Jiraiya summons him, so they could talk about Naruto's key. He wants the scroll go to Naruto since he thinks that he was going to die. Gerotora angrily refuses, believing that Naruto isn't ready, but had no choice.

Post Hunt for Uchiha
Gerotora was one of the toads (Fukasaku, Gamabunta, and Gamakichi) to visit Konoha to bring news of Jiraiya's death.