Gabriel Miller

Gabriel Miller, also known as Subtilizer (in Gun Gale Online) and Vector (in Alicization), is the main antagonist in the second half Sword Art Online: Alicization, known as the War of the Underworld Arc. He is also the final boss of the series' original web series version.

He was first mentioned in Gun Gale Online Arc as the winner of the 1st Japanese Bullet of Bullets, using only a knife and a handgun, and the winner of the 4th Japanese BoB, without bringing any weapons of his own.

He is voiced by Akira Ishida in Japanese version, and by Ted Sroka in English version.

Personality
Gabriel is not only charismatic, manipulative, and wickedly intelligent, even despite his insanity, but also is simultaneously utterly bloodthirsty and utterly devoid of anything remotely resembling empathy. He murdered his fiancée when he was a child to see what the nature of the soul was like, experimented on animals for that same reason also during his youth, and treats his followers either as tools or his own playthings.

Gabriel constantly views everyone else as beneath him whilst discarding them after being done using them for his own purposes. Gabriel has the gall to mock an AI for sacrificing his own life, and then Kirito, Alice, Asuna and Shino for their supposed arrogance, and eventually tries to capture Alice and destroy the Underworld.

Trivia

 * In the web version, it was revealed that "Subtilizer" is an English word, borrowed from French, which in turn was borrowed from Latin, where it means "one who hides things below". Reki interpreted this as "one who steals things away", similar to the French meaning of "Subtiliser", "to steal".
 * In the web version, Gabriel was presented as the final antagonist, because the web version doesn't include the currently onging Unitial Ring Arc, which is reportedly to be the final story arc of the light novel series.
 * In addition, in the web version, the final battle against Gabriel as well as the epoligue happened after the original Moon Cradle Arc was over.
 * Gabriel is by far the strongest villain in Sword Art Online series, and it's justified considering as mentioned above, he was the final boss of the series before being adpated into light novels.