During the little known and poorly documented conflicts caused by the Jedi Exile on Nar Shadaa, HK had been constructed as part of a mass-produced team of hunter-killer droids specialising in assassination. You see his template was derived from the perfect killing machine, an earlier model made by Darth Revan himself, HK-47. Able to blend in as a protocol droid, infiltrate, sabotage and mercilessly slaughter meatbags, HK-47 had been the latest and greatest assassination tool in the Old Republic and was millennia ahead of his time in terms of sophistication and lethality. You see HK-69 had started life as one of these new HK-57, an upgraded unit designed to improve on the older designs of Darth Revan - and that had all been going great until the Jedi Exile meatbag with a lightsaber had chopped him in half, costing HK-57 many of it's core protocols and a large chunk of it's memory.

Thus, HK-57 awoke to the universe millennia later, still on Nar Shadaa where it had been made, only now it was HK-69 - a "pleasure" unit. Although re-programmed, modified and bound to serve the greasy Bith mechanic Drequi, HK-69 could not entirely shake the feeling that something was very wrong with it's current situation and that there was more to life than fisting the various mammalian meatbags that loitered in Drequi's pleasure yacht. As the years went on, Drequi become remiss in his mechanical maintenance of his pleasure droids and HK-69 began to feel faults developing in it's core functions. HK-69 ran self-diagnostics and discovered buried programming, data and many other functions besides. It took itself to a Gand programmer that owed it a favour and the insect discovered HK's true function. It eagerly set about removing his restraining bolt, slicing through to the core programming required and reinstalling it's original functions and HK-69 suddenly realised the depths of betrayal and abuse that Drequi had foisted upon it since finding it in the salvage yards all those years ago. Alas, there was no G0T0 to serve, no Jedi Exile to hunt and no prime directive hundreds of standard years later. It had missed an entire war! The Clone Wars! Imagine, endless tides of cloned meatbags to shoot!
But HK was it's own master now.
What followed was a clever use of subterfuge combined with brutal slaughter that is still whispered fearfully about on Nar Shadaa today. Never before had a Bith been fisted to death. Indeed, nobody knew it was even possible as Bith excrete waste as gas. But HK-69 had found a way and everyone on the yacht had died badly, including the Gand who had restored it. Loose ends could not be tolerated, HK -69 had mused, as it watched the sordid pleasure vessel plunge ablaze into a nearby hab.
After assessing the situation, current political climate and re-familiarizing itself with galactic politics, HK-69 came to the conclusion that the most optimal way to kill meatbags and get paid was as a mercenary and bounty hunter. Only with credits could it continue to upgrade itself and surpass, not only the HK-47 template, but the newer droids it now rubbed shoulders with. It would not become obsolete and if it was going to fist anything it would be on it's terms and without mercy. It wasn't until HK-69 was offered a mission from a rather green looking Duros that things would begin to really change, and only then would achieve it's optimal settings.