Character: Kayaba Akihiko

Kayaba Akihiko is the Director and creator of the Nerve Gear and Sword Art Online, as well as the main antagonist of the Sword Art Online arc. He traps all the players within Sword Art Online by using the Nerve Gear to cease sending signals to the users' body. Any in-game death or attempt at removal of the Nerve Gear would result in the real life death of the user. Later, it is discovered that he has been masquerading as Heathcliff, the leader of the Knights of the Blood Oath. Although he has the admin powers to make his avatar immortal, he is shown to be a powerful player even without his in-game immortality due to his intimate understanding of the SAO game mechanics which he himself had designed. He is defeated by Kirito at the end SAO arc, and at the end of ALO arc, leaves behind a program that grants Kirito the World Seed. His death was his own doing since he had also rigged his own Nerve Gear device to fry his brain when he was defeated and transferring his soul into a digital form.

Source: Wiki