X-1 was a Human male assassin engaged, alongside a group of six others, to take part in Project Omega. This experiment was the brainchild of Commander Rezi Soresh, who sought to engineer the ultimate assassin for the service of the Galactic Empire. Soresh subjected them to facial reconstruction surgery and erased their former identities from a computer database. Subsequently, he initiated a harsh program of reconditioning, intending to transform them into unthinking tools by eradicating their memories and feelings.
Initially, X-1 developed bonds of friendship with X-2, X-3, X-4, X-5, X-6, and X-7, the other individuals involved in the training regimen. Nevertheless, following the commencement of torturing via electrocution by Soresh, X-1, in common with the other trainees, underwent a complete alteration of their personality and mind, leading to a state of emotional detachment. Approximately around 10 BBY, the participants were forced to fight each other until only a single survivor remained. X-7 handily killed X-1 and was selected to become Soresh's personal assassin.
X-1's character was seen in a flashback during Rebel Force: Target, the initial book in the Star Wars: Rebel Force series for young readers, released in 2008 and authored by Alex Wheeler.