HK-77 was an assassin droid sometime during the reign of the Galactic Republic, following the Jedi Civil War.
The HK-77 assassin droid was considered the pinnacle of the HK-series assassin droid line. It was based on the HK-47, HK-58, and HK-65 models. It was slightly shorter than the other models, and had a narrow head with optical sensors that extended from each side of it. Unlike the earlier models, the HK-77 had blaster rifles integrated into its arms for quick and easy access.
It was considered extremely aggressive and preferred overt action to stealth. It would often reveal itself to a target and give it an opportunity to escape or attack first. It cost 19,865 Credits new. A popular modification was to convert the HK-77 into a firefighting droid by replacing the blaster rifles with fire extinguishers and coating the armor with a heat-resistant material.
The HK-77 assassin droid was basically a smaller version of the HK-47 unit made infamous as an ally of Revanuring the battle against Darth Malak. HK-77s were designed to serve as bodyguards or henchmen to larger droids. At least one HK-77 unit found its way into a gang led by HK-47 on Mustafar surviving the Galactic Civil War. One was seen later on in a junkyard by the Second Imperial Civil War.