Relenor is the Varrockian author of the Trivium Daemonum, a reward from the Demon Slayer quest. The book details his containment of at least one Avernic demon, the interrogation of Azacorax, and the knowledge that he learned from them, although much of it is inaccurate. He learned much about Infernus - the homeworld of the demons - although he was told that its true name was Pandemonium, and that the true name of the demon race was Avernic, as opposed to just one of the many demon races.
He also learned about how demons operated, and how they manage to travel to Gielinor from Infernus. When he was last heard of, he was traveling to Karamjan jungles to try and find a greater demons located inside the jungle, which he intended to confront.