Light Yagami is the protagonist and anti-hero of the story. At the start of the series, he discovers the Death Note and uses it to kill criminals, becoming known to the people of Japan as Kira (based on the Japanese pronunciation of the English word "killer"). He is characterized as an extremely intelligent, but bored young man, who is frustrated by the lack of justice in the world. He is confident of his own intelligence and how smart he is in relation to others.
His life undergoes a drastic change in the year 2003, when he discovers a mysterious notebook, known as the "Death Note", lying on the ground. The Death Note's instructions claim that if a human's name is written within it, that person shall die. Light is initially skeptical of the notebook's authenticity, but after experimenting with it, Light realizes that the Death Note is real. After meeting with the previous owner of the Death Note, a shinigami named Ryuk, Light seeks to become "the God of the new world" by passing his judgment on those he deems to be evil or who get in his way. Being a genius, Light feels that only he is fit to judge humanity and steer it on a proper moral course, viewing himself as the "god" of the new world he is creating.
A short time later, Light sets to work ridding the world of criminals, attracting the attention of the master detective L. Light and L encounter each other in a series of battles of wit throughout the first part of the series, though once the second Kira, Misa Amane emerges, L is able to corner them both. After giving up the Death Note briefly to clear their names, he is able to finally have L killed by manipulating Rem into saving Misa's life. With L dead, Light takes up his mantle to keep the world in the dark about L's death, becoming the second L while putting him in the perfect position to continue killing criminals. He comes into conflict with L's true successors, Near and Mello, during this time. After making a mistake in using Teru Mikami as a proxy, Near is finally able to corner Light. Having decided that it is time to end his game, Ryuk kills Light.