"Deff" was a highly trained medic and Clone Commando attatched to the 17th Corps. During a mission Deff's entire squad was killed. He was later re-assigned to Jedi Master Ordan Minoh to aid him on his missions.
When Order 66 was put into effect Deff disobeyed and helped Minoh fight off the Clones and escape. After joining the forces at Jedi Cave Deff formed a close bond with the Clone troopers of the 77th Airbourne who had also disobeyed the order to kill the Jedi.