The 2-1B Medical Surgical Droid known as "Cutter" first came to the Alliance five months before the battle of Yavin. It was part of a cargo of medical droids intercepted by the Alliance before that battle, and was assigned to surgical duty on board the front-line cruiser Crusade. It served in several tours on board the Crusade, eventually evacuating with the rest of the crew when it was destroyed in the Porthello Incident.
From that evacuation, 2-1B-C5 was assigned to the Rebel base on Briggia. Again, the droid served in an outstanding capacity within Briggia base, saving many wounded soldiers' lives. However, due to the terrible nature of war, several troopers had to be "let go" while in the surgical unit. This led to C5's supervisors deleting its incapacity to kill. However, they did put in several safeguards that would stop the droid from becoming violent.
Due to the tenuous position of the Alliance and its forward bases, Briggia base fell under an evacuation order. C5 stayed behind in the medbay, prepping its final passengers for evac, until it found itself abandoned. It was found by a medic on his way out, as he took a final sweep through the base. Unfortunately, Imperial troops had breached the base's perimeter and cut the droid down as the pair made its escape.
C5 was cut in half from the trooper's fire. The feedback short from the shots fried some of his programming; specifically, his safeguards against violence. His secondary systems came back on-line just in time for him to save the medic from capture and himself from destruction. The grateful medic carried the bisected droid to a Y-wing and the pair made it off planet.
For not leaving him, C5 began to call the young medic-turned-pilot "Master," and its effects were not lost on the man. The newly christened "Guardian" took the droid with him to Defender Wing, and the pilots and techs there rebuilt C5's chassis and dubbed him "Cutter." When Guardian transferred to the Liberty, Cutter followed.
Cutter's new chassis features a repulsorlift "bed" that begins at his waist. The bed allows him to hover over rough terrain, and makes him more maneuverable. Two extensions are capable of coming out of the "bed" to create a temporary stretcher capable of carrying a Wookiee. Several new additions have also been added to his body--other medical droid brains have been integrated under his own personality. Within one body, he is his own 2-1B surgical droid, as well as an MD-0 Diagnostic droid, MD-1 Laboratory Technician droid, MD-2 Anesthesiology droid, MD-3 Pharmaceutical droid, and MD-5 General Practitioner droid. Guardian also had a 1PO intelligence added, so Cutter can communicate with any patient.
Guardian disappeared on a classified operation, and Cutter's loyalty transferred to the Liberty's surgical head, Doctor Banarj. While the Rebel fleet gathered before the Battle of Endor, Banarj was deployed to the Redemption. Not wanting to be without his best assistant, Banarj brought Cutter along with him, saving the droid's life as the Liberty was destroyed by the second Death Star soon after. From then on, wherever Banarj went, Cutter followed. After a few weeks, they found themselves deployed to the newly minted CRS Vigilant, weeks before the rest of the remainder of the Renegade Wing pilots would be brought onboard.
When Guardian returned to the Wing after the Battle of Toseng and was assigned a U-wing, Cutter insisted on being on the crew. He is adapting to having less room to maneuver in, but is enjoying the opportunity to be even more on the front line, and to keep one of his ocular sensors on Guardian.
Personality-wise, Cutter is a slow, patient automaton. He takes care of any problem with a gentle, methodical approach that makes him easy to like, but frustrating to deal with at times. He calls everyone "sir" or "ma'am" except when referring to Guardian, who is "Master Adam."