Nova Squad's Demolition Expert.
DarkCut was always extremely good with explosives since he was born, he joined the UNSC out of College, after 6 years of serving as a Artillery Chief, ONI recruited him into the Spartan-VI program, He excelled at all demolition courses and failed all diplomacy classes, he originally was called the Explosives Doctor until he had a mental breakdown and used a knife to create a Very deep 'Dark' cut into his chest and then using that knife to attack other Spartan-VI's.
ONI was barely able to detain him long enough to sedate him and get him medical attention, he has a Dark Scar on his chest that looks like a cut and so was dubbed DarkCut.
Few Spartans remember his incident as ONI rounded most of the Spartans up and neurally blocked the memory's of his actions in the Spartans found with those memory's. only Roughblade remembers in Nova Squad and that is why DarkCut is in Nova Squad, ONI could not block those memory's in RB because RB's own mental damage protects him from the ONI mental conditioning, which is why DarkCut trusts Roughblade, because RB is the only "Free" Spartan.