HK-57

HK-57 was a HK-series assassin droid produced in an old Separatist droid factory on Mustafar under the control of rogue assassin droid HK-47. After flaws in the HK-57 and subsequent HK-67 models were discovered, HK-47 initiated the creation of a new model, the HK-77 droid.

Behind the scenes
This droid model is mentioned in a message recorded by HK-47. The message is available on a datapad called "Droid Factory Records" in the Star Wars Galaxies addon Trials of Obi-Wan, which players acquire during the missions leading up to the confrontation with HK-47 in the Battle of Koseyet.