In one of the final conflicts on the cloning stations at Kamino a group of new recruits, nearly fresh from the vats and still loopy from accelerated training/conditioning are cryogentically frozen and set on a transport that *almost* made it off planet unscathed. Almost.
Weapons fire triggered the ship's hyperdrive before Astrogation coordinates were set and the ship, now crewless due to a hull breach was adrift for nearly a decade before rebels discovered it. They took a chance waking the clone squad - a group of pilots at a time when the newly-formed Alliance sorely needed pilots.
They presented way the Empire treated the clone troopers - from the accounts of troopers working side-by-side with the Jedi to the accounts of them turning on their generals and commanders, sometimes mid-battle. The reactions were mixed. Some found it inconceivable to the point of horror, some maintained stoicism and acknowledgement of a soldier's lot.
All were upset by the careless way the new Empire treated their soldiers and the fall in quality when Clone Troopers became 'Stormtroopers'. But mostly it was the Empire failing to do anything about the built-in expiration date the clone soldiers were designed with [Rapid aging] that sparked their ire.
The Rebels offered the clone pilots a choice. They must have been nervous to await the answer as the clone squad deliberated amongst themselves. Eventually two decided to join the Rebel fleet, bringing a near-mint ARC-170 Heavy starfighter and two phenomenally-trained pilots. The others of the squad claimed the newly mended transport ship and gave assurances they weren't going to report to the Empire, rather, make their own way into the world to try to find a cure for the rapid aging promising to share it with the two Rebel Clone Pilots if they find it.
Clone CT-4320 chose the moniker 'NoOne' given that his designation had every other number BUT the numeral 1, and that he felt estranged in this time.

Redemption: The Player Character seeks to atone for past sins or mistakes by serving in the Alliance. He may have served in the Empire: he may have been a criminal, bounty hunter, or followed some other pursuit that caused him to take actions he now regrets. Helping the Rebellion may be a way to regain his self-worth.
While NoOne's motivation isn't personal Redemption he sees how clone troopers before contributed to the terrible state of affairs in the galaxy. He seeks to do what he can to 'balance that ledger'.

a 10-pt duty. Support - he's still subject to the Clone programming that drives him to be of service to others. It is a strong calling that he gives in to often.
a 10-pt duty. Personnel - ultimately he's protective of the lives of others. He'll take risks himself, almost fatalistically, to prevent others from being in harms way.

NoOne looks young for even a Clone Trooper. Otherwise his appearance matches his cloned brethren. He dresses somberly. At times he can be downright fatalistic and emo, constantly looking for a way to 'make a difference' in the world before his inevitable early death.
He feels irrationally responsible for how the Clone Troopers before him contributed to the evils that plagued the world.