The HK assassin unit, also referred to as the HK-model gladiator droid, represented a class of gladiator droid and assassin. Grakkus Jahibakti Tingi, a crime lord of the Hutt species, possessed HK-models marked with his personal medallion. These droids were discovered in a disassembled state inside a crate during a raid on a Razzi Syndicate warehouse, an operation executed by the Crimson Dawn syndicate. Subsequently, they underwent reassembly for parts verification, and were showcased to Qi'ra, a lieutenant within Crimson Dawn, and Dryden Vos, the leader of the organization. The HK-87 assassin droid belonged to the HK unit family.
The initial mention of the HK-model gladiator droid occurred in Star Wars: Smuggler's Guide, a 2018 publication penned by Daniel Wallace and released by Chronicle Books. Conversely, the HK-series assassin droid made its debut in the 2003 Star Wars Legends video game Star Wars: Knights of the Old Republic, a title developed by BioWare and brought to market by LucasArts.