ALAEKSEJOR DE ZHASTUKOVAN:
A.D.Z. (Codename "Slave Zero") is a Synth (short for synthetic humanoids, also called androids, replicants or artificial humans) created at the behest of the imperial archon Aleksej Stukov, who also gave his DNA and memories so that Alaeksejor would have both his appearance, memories and abilities. In a certain sense, Alaeksejor can be considered the replicant of Aleksej, since he practically equals him in everything, and the two are distinguished only by the eyes (Alaeksejor have cybernetic eyes). Although most clones are used to do the work which machines usually perform in other parts of the universe, Aleksejor was created for a special purpose: not for be a slave of Aleksej, but its extension, to operate and act totally free, in his stead as Rear Admiral and Operations Officer of Flotta Stellare faction and to continue to perform his duties with it, even if Aleksej is no longer present in person anymore with faction.

THE FREEDMEN AND FREEDWOMEN:
The code name "Slave Zero" is also used by the "Freedpeople of the House Stukov", that is, all those men and women saved and freed by Aleksej Stukov from any forms of slavery, including both illegal slavery and Imperial Slavery, throughout the galaxy; and that in gratitude they freely chose to serve the House Stukov, pledging allegiance to it and becoming full-fledged free imperial citizens and members of the House Stukov. From that moment they were collectively called "Freedpeople of the House Stukov" and "Slave Zero" individually. For every 100 members of the House Stukov, there's a 35-40 freedmen and freedwomen. There is no discrimination between "original member" and "acquired member" (freedmen and/or others). All are equal in House Stukov.

THE HERO OF THE LEGEND:
It seems that the Freedpeople have chosen that codename name, inspired by an ancient legend's protagonist hero of 2500:

The legends tells the story of Lu Chen, a sinister world overlord more commonly known as the SovKhan, who rules the Earth from a massive complex called Megacity S1-9. The only resistance to the SovKhan is from an ancient order of warriors known only as "The Guardians". The SovKhan's army is nearly invincible as it is, and it is growing by the day. His most powerful units being 60-foot-tall humanoid robots called "Slaves". The Slaves themselves are grown from a combination of artificially created cybernetic embryos and a mysterious compound called NTR95879, referred to as "dark matter" by the Guardians. The Guardians's only hope of overthrowing the SovKhan and his cybernetic army lies in a single captured and hijacked Slave unit, which will have the mind of a specially trained Guardian agent permanently downloaded into it. That unit will be called "Slave Zero" and he will wages war against the SovKhan's forces throughout every part of Megacity S1-9 with the goal of restoring justice and peace.

This legend was told to Alaeksejor by some freedmen who worked as scientists and who contributed to his "birth". According to the latter, Alaeksejor was very reminiscent of the hero of the legend and soon became the symbol of the freed slave par excellence. For this reason, also Alaeksejor decided to adopt this code name to honor both that hero (whether he existed or not), and those who believed in him. Subsequently, Alaeksejor became the head of the division of the Praetorian Guard composed entirely of freedmen who decided to serve as the House’s armed forces.

Therefore, the code name "Slave Zero" can refer both to Alaeksejor De Zhastukovan and to the freedmen who serve the House of Stukov