Background
Born on Coruscant in the heart of the Empire, Orson always wanted to serve in the Imperial Military. He grew up consuming Imperial propaganda, and was proud to be selected for the Academy, where he studied and trained. He showed promise as a pilot, and joined the fight against the Rebels.
In the war, Orson made a name for himself as a particularly ruthless pilot, racking up an astronomical number of confirmed kills and successful runs. He never took killing or bombing too personally; to him, it was just a way to serve his pride and earn accolades. From a starship, it's easy to ignore the humanity of your enemy, and to ignore the wreckage you leave behind.
That changed when Orson crash-landed behind enemy lines after a successful bombing run on a Rebel-occupied planet. He might have died in the wreckage of his TIE-Fighter if an Ardennian scrapper hadn't come to salvage it for parts. Despite Orson's initial hostility, the Ardennian scrapper Tuko helped Orson recover from his injuries, and taught him many things about mechanics. Tuko was particularly fond of building & repairing droids and sometimes reprogramming them, giving even hostile ones new purpose. This inspired Orson to fight his years of Imperial propaganda and reprogram himself to find a new, better purpose.
Orson spent a long time learning under Tuko, about salvaging and repairing tech and droids, and together, they labored to help the survivors of the planet rebuild, though it's a shadow of what it once was, and he was never fully embraced by the native people.
Motivation
Orson brought death and destruction down upon the Rebel cause for years, and was proud of it. After seeing it firsthand, walking on the scorched earth he left behind, Orson was horrified at the reality of what he had done. He wants to make amends, but has no idea where to begin.