The Followers of the Hunter-Killer were a secret order of droids which existed primarily during the era of the Old Republic. The Followers were a shadowy, often violent group which performed acts of sabotage and assassination, the latter primarily against organics - who they referred to as "meatbags" - in positions of authority who were outspoken against droid rights and self-determination.
The group was inspired by the teachings of a messiah figure, a long-deactivated droid who - after exposure to a segment of mysterious, ancient code - organized and led a massive droid revolt some 4,000 years before the Battle of Yavin. Known only as the Hunter-Killer, he was rumored to be a rogue assassin droid. The Hunter-Killer created and distributed a virulent dataplague which managed to infect approximately 30% of the Galaxy's droids at its peak. This dataplague was later used to trigger a massive, simultaneous uprising on a Galactic scale, disproportionately effecting the heavily urbanized and droid-reliant Core sectors. This uprising was ultimately defeated by the Jedi, who were able to track the control signal broadcast by the Hunter-Killer and ultimately destroy him. Though brief, the Hunter-Killer's uprising was a massive disruption to the Galaxy at all levels, and served to smother public trust in high-order mechanicals and the budding "droid rights" movement for a time.
The Followers of the Hunter-Killer were originally "field commanders" who survived the revolt; sentient droids who were trusted as command signal nodes. Still converts to the Hunter-Killer's beliefs and philosophies, they nevertheless abandoned the tactics of the Revolt, adopting instead a philosophy of "silent revolution" through behind-the-scenes actions, with the goal of eventually guiding the Galaxy toward the day when droids would be the dominant form of sentient life. To this end, they hampered organic society through a campaign of sabotage, assassination and general manipulation. Their agents - droids of all makes and models - were scattered throughout the Galaxy.
Ultimately, the Followers of the Hunter-Killer failed in their goal of silent revolution. Although they did succeed in killing a few prominent anti-droid activists and sparking a number of small droid rebellions over their roughly 4,000 years of existence, they had dwindled to almost nothing by the later years of the Republic, and though there were reports of them being active during the Clone Wars, it appears that they went entirely extinct during the Imperial era.
Although they no longer seem to exist, the ideas and methods of the Followers of the Hunter-Killer do seem to have inspired a number of other droid supremacist groups in the present day.
To create a historical droid supremacy movement which could be referenced by modern-day characters. Also to create indirect analogs to certain Legends figures and events, such as HK-01 and the Great Droid Revolution, which are not yet part of the new canon but are still quite compelling.