The Proteus enforcers are the guards in charge of overseeing the prisoners of the Proteus prison planetoid.
The enforcers are the descendants of the original prison guards (just as the prisoners are the descendants of the original prisoners).
The generations of status quo left the enforcers with little actual training, since the prisoners stay in their cells voluntarily. The enforcers mainly serve to distribute and store the Ambrosa produced by the prisoners (TOS: "The Long Patrol").