What is Distortion Tone - First there was the Fuzz Tone, then the Overdrive Tone, and the Distortion Guitar Tone. Distortion Guitar Pedal tone is basically a more aggressive tone to Overdriven Guitar Tone which simulates an Overdriven amp. If you took a Marshall in 1975 and turned it up you would get the sound of Overdrive from driven tubes. Great classic rock sound, classic tone that has been emulated 1000s of times, but in 1975 MXR, Boss, ProCo Rats arrived that gave us the distorted tone. This was new, amps didn't produce this tone on their own, this aggressive biting distortion for hard rock, metal, lead tones etc.

If you really follow these pedals introductions, you will find a parallel to the music of the day. The pedals arrive and New British Metal arrives pretty much a few years later with this balls out aggressive distorted bar chord thunder ! This is what gear and guitar pedals do, as new tones arrived players took them and created new forms of music and expression with them. Now we could argue that the Big Muff was before this but that is really a overdrive fuzz, all though a fat killer aggressive tone it is not the tight, articulate distortion starting in the mid 70s.