Nobuyuki Sugou

須郷伸之, Fairy King Oberon

Originally selected by Asuna's father to marry Asuna, he was adopted into her family on her father's wishes. He attended the same school with Kayaba Akihiko, who he viewed as a rival. During the Sword Art Online incident, he took advantage of the chaos to steal test subjects for research along with Asuna. In ALfheim Online he adopts the persona Fairy King Oberon As the Fairy King Oberon, he keeps Asuna locked up in a bird cage at the top of the World Tree. In the real world, he confronts the powerless Kazuto by voicing his intentions of wedding the unconscious Asuna. While keeping Asuna locked up in ALO, he constantly visited her just to fool around with her. From his actions, one could say that he is a pervert.

After Kirito manages to ascend the World Tree, Oberon and Kirito have a devastating fight. By using his system commands, Oberon is able to completely dominate Kirito. Fortunately, Kayaba Akihiko saves Kirito by overriding Oberon's authority. Then, in the real world, Sugou attempts to kill Kirito when he is running to Asuna's hospital. This backfired and ended up with him going to prison.

(Source: SAO Wiki)