Nobuyuki Sugou, also known as Alberich or Fairy King Oberon, is a major antagonist of the light novel/manga/anime series Sword Art Online. He is Asuna Yuuki's ex-fiancee and former lover, the former director of RECT Inc., former ruler of the VRMMO game ALfheim Online and archnemesis of Kazuto Kirigaya also known as Kirito.
Originally selected by Asuna's father to marry her he was soon adopted into her family on his wishes. He attended the same school with Akihiko Kayaba aka Commander Heathcliff who he viewed as his rival. Once Sword Art Online was cleared, he was able to hack into it via the routers and obtain the minds of three hundred out of the surviving six thousand, one hundred and forty-seven SAO players including Asuna as test subjects for research on controlling people's feelings and memories; in other words research on the manipulation of human souls. In ALfheim Online he adopted the persona of Fairy King Oberon.
As Oberon he kept Asuna locked in a birdcage at the top of the World Tree; in the real world he confronted Kazuto by voicing his intentions of wedding her. While keeping Asuna locked up he constantly visited her and brought her to the verge of tears by harassing her and making her aware he held full control over the virtual world.
After Kirito managed to ascend the World Tree and reach the cage Oberon appeared and used his administrator privileges to keep Kirito and Asuna pinned down with gravity magic. Once they were unable to move he used a menu to call down chains to shackle Asuna. After Kirito voiced his protest he used his own sword to stab him and turned the pain absorber down so Kirito and Asuna experienced real pain. Oberon then sexually assaulted Asuna in front of Kirito by removing her robes, licking her tears and groping her. Fortunately a digitized Kayaba saved them by giving him the details necessary to log in with Heathcliff's ID which due to ALO being an exact server copy of SAO had greater system authority; this allowed Kirito to use a Voice Command to nullify Oberon's supervisor status.
After this Oberon tried using a Voice Command to generate Excalibur, the strongest weapon in ALO for himself but to no avail. After Kirito repeated the same command and gave the generated Excalibur to Oberon he used another Voice Command to deactivate the pain absorber causing every injury to feel as if it were real. Even though Oberon tried attacking his rage and lack of experience left an easy opening Kirito used to strike his cheek. Afterwards Kirito lashed out with his accumulated anger by amputating his foe's hand, bisecting him and then stabbing his head through his eye killing his avatar.
In the real world Sugou attempted to kill Kazuto with a knife when he was going to the hospital where Asuna was being cared for. Even though he was in control for a while and had the chance to deal a fatal blow the pain of his eye which was stabbed in ALO with no pain absorption caused him to miss. Kazuto mustered the strength to overpower him and proceeded to take the knife pointing out that despite it having not real weight or length he could easily kill Sugou. Sugou attempted to run for his life only to have his head slammed into a car with enough force to leave an indent. As Kazuto thought of all the things Sugou had done he was tempted to kill him only to decide he did not have the right to such decisions anymore and should let the law choose his fate. Eventually Kirito reported this and Sugou was found, arrested and sent to prison where he attempted to pin the blame on Kayaba but after an employee was questioned he confessed and revealed the full extent of his plans to the world which led to the downfall of RECT, its fellow companies including the remains of former SAO owner Argus and the world of VRMMOs.
In the Legacy of Chris Thorndyke he was freed from his prison by Ganondorf’s soldiers and was experimented on by Wesker and has a special gadget to change from his real world self to his Avatars and he killed Asuna’s Parents, first Shouzou Yuuki by shooting him in the head and then Kyoko Yuuki by torturing her and even said that looks like her plan had failed while he laughs manically and also hired the Laughing Coffin to kill Yuuki Kouichirou, until his plans were failed, since Vassago Casals works under a higher rank, according to Ganondorf and tended to do him away by General Onox.
And he is reprised by Todd Haberkorn in the English dub and Takehito Koyasu in the Japanese dub.