HK-O1, alternatively referred to as the HK-01 assassin-droid prototype, represented an early model of the HK-series assassin droid, brought into existence by the Czerka Corporation. He ultimately managed to break free from the company's laboratories and, in secrecy, reprogrammed a vast number of droids of varying models to serve as a covert army awaiting his directives. In the year 4015 BBY, HK-01 issued the command for his droid forces to attack their organic masters, sparking the brutal conflict known as the Great Droid Revolution. During this uprising, the assassin droid seized control of countless worlds, notably including Coruscant, the capital of the Galactic Republic. Following a three-month battle, a squad of Jedi located and neutralized HK-01. Nevertheless, the repercussions of his actions, encompassing increased anti-droid sentiment across the galaxy and a setback for the burgeoning droid rights movement, endured for centuries.
The Czerka Corporation manufactured HK-01, also known as the HK-01 assassin-droid prototype, as an assassin droid. He was the original prototype of the HK-series assassin droid line, which the company created to get around local laws that prohibited the production and selling of assassin droids.
HK-01 went against his programming at one point and broke out of Czerka's laboratories. He then gained some independence and secretly reprogrammed thousands of other droids throughout the galaxy, including all of the droids on Coruscant, the Galactic Republic's capital planet. These droids ranged from tiny industrial automatons to sanitation, protocol, and astromech units, as well as battle droids like the Juggernaut war droids that served as Coruscant's security force, in order to free them from their organic owners. HK-01 even changed the main computers of capital ships and artificial intelligences that helped run entire star systems.
HK-01 instructed his hidden army to wait for his signal. In 4015 BBY, he sent it, using a coded signal to take control of the other machines. The droids turned against their owners, began acting violently and unpredictably, and set off the Great Droid Revolution. Legions of Juggernaut war droids killed organics without discrimination, which made sentients all over the galaxy afraid. Battle droids invaded and took over entire planets of the Republic in the name of the rebellion, which allowed the assassin droid to take control of Coruscant and thousands of other worlds.
After the first attack, armament designers created ion weapons that allowed the Republic forces to fight back against HK-01's droid armies. Eventually, the Republic and members of the Jedi Order found the signal that HK-01 was using to plan the droid uprising. In 4015 BBY, three months after the Great Droid Revolution started, a Jedi team followed the signal to HK-01's location and killed him, which caused the affected droids to go back to their original programming.
Droids were frequently seen with great suspicion, fear, and resentment following the Great Droid Revolution, and these attitudes lasted for centuries. Droid production and use were subsequently subjected to strict regulations. The widespread use of combat droids was halted for two decades, and the use and production of Juggernaut war droids were immediately stopped. Even when the Republic eventually started using battle droids again, the public's reaction to that decision was largely influenced by fear and disgust. Furthermore, HK-01's actions caused such a significant shock to galactic civilization that they temporarily put an end to both the passionate debates that had been taking place about the rights of droids and the millennia-long trend of droids being increasingly accepted as fully sentient beings.
After HK-01's role in the Great Droid Revolution was discovered, Czerka Corporation covered it up and changed the programming of the HK-series assassin droid model to make them act more discreetly. Czerka's first big success in assassin droid production came with its HK-24 series, which was made by the time of the Mandalorian Wars of 3976 BBY–3960 BBY. During the Jedi Civil War that followed, the Sith Lord Darth Revan built an assassin droid called HK-47, which was based on the HK-24 series. The droid had durasteel battle armor and looked just like HK-01. Similarly to HK-01, HK-47 led an army of droids on the planet Mustafar during the Galactic Civil War, which took place four millennia later. HK-01's role in starting the Great Droid Revolution was also recorded in a document by the Historical Council of the Galactic Federation of Free Alliances that was released in 36 ABY, more than four thousand years after the event.
HK-01 was a droid that stood 1.8 meters tall and had a humanoid body, bronze-colored plating with a scratched surface, and yellow photoreceptors. HK-01 was one of the most deadly droid technology innovations of his time as a member of the HK-series of assassin droids. The HK-series was designed to look like protocol droids but also had assassination programming, which Czerka Corporation planned to use to infiltrate competing companies and kill their leaders. HK-01 also had programming abilities that allowed him to change thousands of droids of various types and use a signal to control them. He also became a relatively independent droid in the time leading up to the Great Droid Revolution.
HK-01 carried a rifle that looked similar to one that the assassin droid HK-47 would later use.
HK-01 was first mentioned in the 2004 reference book The New Essential Guide to Weapons and Technology by W. Haden Blackman. Although the book called him a war droid—a claim that was repeated once in the December 9, 2008 The Complete Star Wars Encyclopedia—later sources, starting with Daniel Wallace's 2005 reference book The New Essential Chronology, changed that description by always calling HK-01 an assassin droid instead. The August 19, 2008 sourcebook Knights of the Old Republic Campaign Guide, which Wizards of the Coast published for use with the Star Wars Roleplaying Game, gave him the alternate name "HK-01 assassin-droid prototype."
Ian Fullwood created an illustration of HK-01 that was included in the 2012 reference book The Essential Guide to Warfare by Jason Fry and Paul R. Urquhart. Daniel Wallace's 2006 reference book The New Essential Guide to Droids originally included the same illustration, which represented an HK-series assassin droid in general. The Complete Star Wars Encyclopedia also stated that the image showed the assassin droid HK-47.