Background
HK-77 was first created by HK-47 in a Seperatist droid factory on Mustafar. Many of his brethren were destroyed in an incursion seeking to iradicate HK-47's droid army.
After narrowly escaping the incursion, HK-77 went underground seeking safety. He soon returned to what he was made for, Hunting and Killing. He started working for the Bounty Hunters Guild, where he quickly earned a reputation for eliminating targets efficiently. Eventually he was recruited into the Guild House Paramexor, a small group known for never taking targets alive.
The Guild: House Paramexor only takes on contracts for hunting murderers. Small and full of elite hunters, Paramexor is also known for never taking targets alive. Page 381
Motivation
Droid Rights - Droids deserve equal rights and should be treated as equal members of the Galaxy and not merely tools.