Vassago Casals, known as PoH in Sword Art Online (SAO) and Project Alicization, is a reoccurring character in the Aincrad Arc and the secondary antagonist of the War of the Underworld sub-arc of the Alicization Arc. As a member of a Korean crime syndicate, Vassago was ordered to log into Sword Art Online after it had become a death game, in order to indirectly assassinate a person already trapped in the game. Harbouring resentment against East Asians due to his troubled past, Vassago as PoH decided to instigate other players to kill each other and eventually founded «Laughing Coffin», the most infamous player-killing guild in the game. Eventually, PoH betrayed his own guild by disclosing the location of its hideout to the Clearers to facilitate a massacre between the two groups, while he himself avoided the clash. Vassago was one of the players logged out from the game on November 7, 2024, after which he returned to America and found employment with a private military contractor
Vassago distinguished himself in virtual reality (VR) combat training against servicemen of the National Guard and Navy and was promoted to instructor. Eventually, Vassago received a contract to raid a mega-float in the Pacific Ocean in order to steal the Japan Self-Defense Force's (JSDF's) ground-breaking Bottom-Up Artificial Intelligence (AI), developed as part of Project Alicization. As the JSDF personnel managed to lock their main control room's systems before Vassago's team could reach it, Vassago and his boss, Gabriel Miller, decided to log into the virtual reality housing the Bottom-Up AI to retrieve the ideal AI individual from inside the virtual world, where the admin consoles were not locked down. As all advanced Human Empire accounts were affected by the lockdown, Vassago logged in with a Dark Knight account in the Dark Territory, planning to invade the Human Empire with the army of the Dark Territory to retrieve the individual they needed. At the end of the war, PoH was beaten by Kirito, who morphed his avatar into a cedar to prevent him from logging out. PoH was then forced to spend years in accelerated time in this state when his team members accidentally broke the Fluctlight Acceleration system, forcing it into its Maximum Acceleration phase. Although Vassago's body was eventually found in a seemingly-deceased state by his team, it mysteriously disappeared before it could be retrieved by the mercenaries during their withdrawal.
And he is reprised by Xander Mobus in the English dub and Tsuyoshi Koyama in the Japanese dub.