The EH Muff series of fuzz boxes has almost as much mystique & hype surrounding it as the Ibanez Tube Screamers. They go way back to the early '70's and were used by many of the big names. There are several prized vintage versions, and you'll come across statements about how the "Ram's Head" versions were better or worse than the "Triangle" versions, or that the Russian pedals are better/worse than the US-made ones, yada, yada, yada....
There's even a Wikipedia entry:
http://en.wikipedia.org/wiki/Big_Muff
Personally, I'm not a big fan of the Muff sound, but a lot of players love 'em. I built a clone kit version of the Triangle era Muff and modded it to add some tonal flexibility, but it just never grabbed me. I sent it to Tone for him to check out (before he bought this one that he just sold), but the good ol' US Postal Service managed to lose it. And (like an idiot) I didn't send it insured.... :reallymad: