This is the Version 2 Big Muff, commonly known as the Ram's Head. It shares many similarities with the earlier “Triangle” Big Muff and delivers a cranked-amp style tone, though with a slightly different sweep on the tone control. This version is famously associated with David Gilmour and is widely believed to be the one used on “Comfortably Numb” and The Wall album.
The pedal is all original, showing only mild signs of play wear. Note that it uses the older-style on/off switch, so be sure to check it after use to avoid draining the battery.