I'm not sure who originated the drink. Perhaps it was Nash's, a Limerick soft drinks company founded in 1875. According to their website:
One product, however, has remained favourite locally – Nash's Red Lemonade. No farm worker's lunch was complete without a bottle of the unique fiery coloured drink. To this day the formula for this refreshment remains a closely-guarded family secret.It's a lemon-flavoured drink but distinct in taste from white lemonade. As a drink on its own it is not very popular these days but it's commonly used as a mixer, especially in whiskey. In the 1980s, Paddy whiskey was the first major brand to encourage the use of mixers in a very successful campaign.
To this day, you can order a "Paddy and red" or "Jemmy (Jameson) and red" in any Irish bar.
Several companies make red lemonade today, besides Nash's. One of those is C&C, whose TK brand I was using as a mixer in the Dundalgan test. C&C also happen to own the Tullamore Dew brand of whiskey.
TK red lemonade was the only brand I could find in my local supermarket so this was the one I used in the Dundalgan test. Unfortunately it tastes pretty awful, with that familiar aftertaste characteristic of artificial sweeteners. For some reason TK contains sugar, aspartame and saccharin and the result is just as good as you would expect.
Don't let that put you off trying a whiskey and red though. The version available in bars is unlikely to be TK and is, I hope, of better quality. I'll keep an eye out on my field trips and report back.