Aravv was an ancient Toa Lorekeeper of Justice, and one of that Lore's primary heroes.
Aravv was one of the first Toa of Cortan-Nui. His element was fire, and used it to burn away anyone who broke the law. Soon, the toa realized that Cortan-Nui was in no real danger, and they left the island, seeking a place in need of their kind. Aravv soon broke away from the rest of the group, for unknown resons, and took a boat out to a Lore-Controlling organizations fortress:
The Keepers of Peace.
There, it was revealed to Aravv that he possessed a powerful Lore known as Justice, and that it was very dangerous. Aravv trained under the Keepers, until they decided it was time to test him. They brought out a murder, a Piraka, and told Aravv to execute the crying beast.
He did so without a second thought.
Later, after Aravv left the Keeper's fortress, he went to a forgotten island. After all of his travels, he had lost much of his sanity, and decided that the entire island was corrupt. He began, at first, to kill the Evil-Doers. But soon, he began to kill those who did not do anything wrong.
After killing thousands, his sword of Justice, began to become angry. One night while Aravv was sleeping, his powers took over, and caused the Lorekeeper to kill himself.
This story is told by The Keepers of Peace, and by Lorekeepers of Justice. It is a tale that advises them never to abuse their powers, for they will turn against you if need be.