Actually the question is not so much who as what?
Ralf has roots in darkest Dorset some 25 years ago, when a group of four CAMRA activists decided that the campaign wasn't militant enough, while the four Dorset brewers were dragging their heels over pressurised beer. The result was a secret cell going by the name of Ralf: Real Ale Liberation Front.
Various forms of action were discussed, including blowing up pubs, and even drilling holes in the CO2 tanks at BOC. The first of these was ruled out because the ale itself was actually very good; the second because it was a bit dangerous, to say the least! Though had cordless drills been available then...
Eventually a course of civil diobedience was drawn up: pubs serving pressurised real ale were entered, pints were ordered and (depending on the size of the landlord) refused, and Ralf stickers were slapped on glasses.
The result: Ralf was barred from so many pubs that he nearly had to give up drinking! But time passed and handpumps began to appear. Real ale was returning, good pints abounded and Ralf was disbanded - but he was still barred!