A Vintage Big Box ProCo The Rat Overdrive/Distortion from very early 80's with the highly sought after LM308 op amp chip. With the ability to get tones from clean boost, through lovely smooth overdrives, to nasty as hell high gain distortion. This is the pedal that made the Rat famous, with users as disparate as SRV, David Gilmour, Dave Grohl, Frank Black, and Trey Azagthoth. Even James Hetfield reportedly used one for Kill 'em All.
Nasty and nice it's a dirty rat.