[quote=idlehands]
Who, not what. I'm assuming someone in the thing where that deathnote thing came from.
[/quote]

A summary from Wikipedia of Light:

Light Yagami also known as Kira, is a fictional character in the manga and anime series Death Note. He is a bored young genius who finds the Death Note dropped by the Shinigami Ryuk by pure chance. 

When Light discovers the Death Note, he begins a crusade against evil, planning to kill criminals and other ne'er-do-wells until only those he approves of are left. While his task is well-intentioned, he is corrupted by power within a week, plotting to rule his utopia as "the god of the new world".

His ethics are utilitarian, justifying the most extreme acts in service of his cause. He is also driven by a need for victory, which motivates most of his cruellest acts. Combined with the power of the Death Note, his hubris and genius-level intellect convince him that only he can save the world.