HK-47 is a fictional assassin droid from the 2003 video game Star Wars: Knights of the Old Republic, its sequel, Star Wars: Knights of the Old Republic II: The Sith Lords, and the Trials of Obi-Wan expansion pack to the massively multiplayer online game Star Wars: Galaxies.
In Knights of the Old Republic, the player's character purchases HK-47 on Tatooine. Dialogue establishes that Revan built the bloodthirsty droid, which characteristically refers to organic lifeforms as "meatbags".
HK-47 is disabled at the beginning of The Sith Lords; the player's character recovers material from damaged droids to repair HK-47. Dialogue in The Sith Lords expands on the droid's backstory and purpose, establishing that Revan used the droid to kill people who destabilized or weakened the galaxy.
In the time frame of the Trials of Obi-Wan expansion to Star Wars Galaxies, HK-47's artificial intelligence has transferred into a computer on a Galactic Republic cruiser that later crashed on Mustafar. The droid calls on players to complete several quests to return him to a droid body.
Source: Wikipedia, "HK-47", available under the CC-BY-SA License.