Yahiko

is a deceased ninja from Amegakure; his body acts as the Deva path of Nagato's Six paths of Pain.

Background
Yahiko, along with Nagato and Konan, was left orphaned by one of Amegakure's many wars when they were children, forcing them to fend for themselves. The three eventually encountered Jiraiya, who looked after them and taught them basic ninjutsu. Nagato watched a Stone Chunin injure Yahiko and killed him using his Rinnegan, in a berserk rage. Yahiko has a strong "eye for an eye" philosophy (that was adopted by Nagato after his death), and hates the way Amegakure is looked at by the rest of the world and hates what it has become. He is defensive of the village, saying that his dream is to stop the endless rain, which he compares to tears, and protect the nation's citizens. He has the ability to use water-based jutsu. Sometime after Jiraiya's departure from Amegakure, the three quickly gained a reputation. At an unknown point in time, Yahiko died, so Pain was able to control Yahiko's body as his own, while probably the trauma of loss made Pain follow most of Yahiko's dreams, as well as the eye for an eye way of accomplishing them.

Abilities
The water jutsu he is able to use seems to shoot a jet of water from Yahiko's mouth.

Trivia

 * Yahiko apparently died around the age of 25-30 since a dead body cannot age.