R6-T4 was created by Industrial Automaton as one of several prototypes that were meant to entice certain influential individuals to sign extended contracts for the future mass production of the R6 series. R6-T4 was designed with Gran Moff Tarkin in mind. It had been delivered to the Moff's personal assistant's hands and on route to the Death Star for final delivery to the Moff when the Imperial base was destroyed. Rebel forces from Yavin captured the shuttle carrying the prototype and commendeared the unit.
R6-T4 was a state-of-the-art prototype programmed to serve as an assistant to high ranking commanders. This was something he strongly voiced when he was being re-purposed as common mechanic and snub-nose fighter astromech. This did not ingratiate him with the mechanics, including another astromech named Rusty who took to mockingly calling him Commodore 64.

Belief: The Republic
When captured by the Alliance, 64 was reprogrammed with a strong loyalty to the Alliance and the restoration of the Republic. This wasn't too hard to do. Just switching a few 1's for 0's to replace his Imperial loyalties to Republic ones.

Quest: Glory
As part of his basic programming 64 feels a strong need to stand at the side of a powerful leader and help him to succeed in all his endeavors. As such he seeks glory for himself so that he may rise in people's estimations and be noticed by such an individual. Also he is drawn to the side of whoever is the current leader to help them in anyway to achieve victory and recognition.

Tech Procurement: 0 pts
As a state-of-the-art prototype 64 strongly feels that newer and faster is better. Whether it is stealing battle station plans or boosting a prototype hyperdrive system or modifying a shield generator, all of it in for the purpose of gaining the advantage over the enemy.

64 is a shiny silver unit with black trim. Or he was until the Alliance got ahold of him and started adding mechanic modifications with a little less gloss. It hasn't been much, just some tool arms and plating, but it has been very off putting to 64.
If it were possible to speak binary with an Imperial accent, 64 would. He was programmed to be the perfect Astromech compliment to any proper Imperial Admiral. He puts due attention on decorum and rank. This gives him an air of snobbery that other droids and mechanics don't appreciate.