Ryuk is a shinigami, a god of death. He seems to be somewhat of an outcast in the shinigami world. He is clever to the extent that he was able to trick the Shinigami King into giving him a second Death Note. He seems to have done this because he is tired of the Shinigami Realm; he considers it to be rotten and boring.

To end his boredom, Ryuk drops a Death Note into the human world. He wrote instructions for its use in English because it was the world's most common language and he did not know who would pick up the note. Five days after dropping the note, Ryuk set off to the human world to find the person who picked it up.

Like any shinigami who has his note taken by a human, he must stay by that human. Ryuk's note was taken by Light Yagami who uses it as Kira. While with Light, Ryuk enjoys playing video games, watching Kira's plots unfold, and, above all else, eating apples.