Heathcliff

Heathcliff aka Akihiko Kayaba (voiced by Kevin M. Connolly) is the creator and Anti-Hero turned guide for Kirito in Sword Art Online.

Pre Adventure Series
He created Sword Art Online which trapped 10,000 people trapped for two years and upon his defeat set free, and helped Kirito to rescue Asuna. Kayaba also created the NerveGear, and The World Seed. Kayaba also created the Guild, The Knights of the Blood Oath.

Adventure Series
Heathcliff was once known as Kayaba, and was a good friend to Asuna Yuki's family, often spending time with the group. Then that all changed when The Heartless attacked, the result of an experiment done by his former assistant, Sugou Nobuyuki. He managed to escape but the effect caused him to change in his appearance, and take in Asuna as a pupal upon her request. The two created The Knights of Blood Oath to combat the Heartless, until hearing and meeting Kirito, who became a valuable ally in their fight against the Heartless. When the two returned from being attacked by Darkside, the two asked if they can get married, which he agreed, and changed his name to Heathcliff. He even welcomed their new daughter Yui.

Trivia

 * Heathcliff will appear in the near future.