The 103rd Nightbrothers were an elite battalion of clone troopers trained by their commander CC-1010 a.k.a. Commander X. They never lost more than 30 men in the entire clone wars. The battalion was led by Commander X, General Val Kepros, and Lueitenant Brazier. Commander X wiped out the entire battalion on Vardos when they conrnered a surviving jedi with the last member of the battalion being CT-5810 (The guy on screen). X suffers from PTSD for slaughtering his entire team.
Shredder got his name from his preference for the Z-6 rotary cannon he wielded extremely effectively. He fought with the 103rd throughout the majority of the clone wars, fighting loyally and bravely. However, he would be separated from his battalion one mission, where he would save bounty hunter, the Black Talon or Triss's, life. The two ended up working together to survive for a couple of months, before Shredder officially deserted and became a bounty hunter alongside his friend. After Order 66, without any jedi nearby, he ignored the order and its effects wore off like other clones. And after he discovered what X did to the nightbrothers, he developed a personal grudge and hatred towards him and his extremely shifty loyalties that never remained with his brothers. He then changed his name from shredder to Buurenaar [boo-REY-nahr], or storm in Mando'a
