Pro Co is the American company behind the RAT family, one of the clearest examples of a distortion circuit becoming a category reference. The catalogue here includes RAT 2, Lil’ RAT, Turbo RAT and the Sterling Vermin, each shifting the basic recipe through size, gain range, clipping or voicing. The core idea is hard-clipping distortion with a filter control that shapes the top end, so the pedal can move from grainy overdrive into compressed, cutting distortion. Compare model-specific headroom and low-end response before assuming every RAT behaves identically.