Akihiko Kayaba, the primary developer of the virtual reality MMORPG Sword Art Online and its NerveGear access device, possessed an academic background rooted in mathematics and university laboratory work rather than gaming. Prior to the SAO incident, he served as executive director at game studio Argus, driving the company's success through his dual expertise as a game designer and quantum physicist. He personally architected SAO's foundational systems, including the Cardinal System, and later created "The Seed," a package enabling others to build virtual worlds. His core motivation stemmed from a childhood dream: creating the floating castle Aincrad. Upon achieving this vision within SAO, he initiated a death game to observe human behavior under duress. On November 6, 2022, he trapped approximately 10,000 players within the game. Manifesting as a colossal, faceless hooded figure, he announced the lethal rules: death in-game or forced NerveGear removal meant real-world death; clearing all 100 floors offered the sole escape. Within SAO, Kayaba operated under the alias Heathcliff, adopting an avatar deliberately contrasting his real appearance – muscular, tall, with steel-gray hair. As leader of the Knights of the Blood guild, he wielded the Liberator sword-and-shield set and possessed the unique "Holy Sword" skill, granting near-impenetrable defense. He maintained invincibility by exploiting a system loophole preventing his HP from entering the yellow zone, earning titles like "The Strongest Man" after battling the 50th Floor boss single-handedly for ten minutes. While aiding players in clearing floors, his ultimate plan involved revealing himself as the final boss on Floor 100 after Floor 95 was cleared. Kayaba exhibited intellectual detachment and disregard for human life. He ensured SAO remained a beatable challenge with calm fairness, yet showed no remorse for fatalities, including Asuna Yuuki's apparent death during his duel with Kirito. After Kirito exposed his identity on Floor 75 and defeated him in combat, Kayaba honored their agreement, freeing all survivors. He then utilized a modified FullDive machine to scan his brain, transferring his consciousness into the virtual world. This process destroyed his physical body, resulting in real-world death. His consciousness persisted digitally. During the Fairy Dance Arc, drawn by Kirito's voice during a crisis, he resurfaced within ALfheim Online (built from SAO's data). He provided Kirito with administrative credentials to defeat Oberon (Sugou Nobuyuki) and entrusted him with "The Seed" to proliferate virtual worlds, highlighting his enduring fascination with human will and virtual existence. In non-canonical portrayals (e.g., games Infinity Moment and Hollow Fragment), Kayaba's Heathcliff avatar encountered system glitches during the Floor 75 duel. Following these events, he acknowledged players' collective resilience as a potential unconscious motive for creating SAO.