Light Yagami is a top of his class high school student (at the beginning of the series, later on he graduates) who has possession of a notebook (called the Deathnote) that will kill anyone who's name is written in it, as long as the correct person's face is being pictured in the writer's mind. By default, the target dies of a heart attack 40 seconds from the time the name is written, but the owner can specify the cause and time of death by simply writing those details in the notebook.