The pilot of the AC, Nine-Ball, he has been the top-ranked Raven in the Arena since its inception. Not much is known about this figure, as few Ravens are willing to challenge him and he rarely accepts missions. One fact though remains undisputed - he is a force to be reckoned with and displays few, if any, weaknesses. Serving as the main antagonist of Armored Core: Master of Arena, it was he who killed The Raven's family and as a result of this, the Raven joined the Ravens' Nest in order to take his revenge.

In truth, Hustler One is merely the designation given to a super-advanced AI as revealed in Armored Core: Master of Arena

Nine-Ball and its pilot, Hustler One, are the main goal of the game as the reigning champion of the Arena as well as the main antagonist according to The Raven, whose family was killed by Nine-Ball. Thus, The Raven enters the Ravens' Nest in order to eliminate the man behind. Its pilot, Hustler One is simply an advanced combat AI and its AC, Nine-Ball is being mass produced. Its purpose is later revealed and can be best described as being similar to The Controller in that it was created to allow humanity to continue existing; in fact, much of the infrastructure, the organizations (Ravens' Nest, the corporations), as well as the conflict between them were created and manipulated by this AI. Despite this, The Raven manages to defeat Hustler One and becomes the #1 Raven in the Arena, and is given the title Nine Breaker. The Raven, Leos Klein, would later become the main antagonist of Armored Core 2. His pilot description is "The strongest undefeated Raven, he is both feared and sought after by those ranked below him.". He appears in the mission Eliminate Fugitive and is fought in the mission Defend Laboratory, Eliminate Intruders and finally in Enter Factory.