Regan's Orange Bitters are the creation of bartender Gary 'Gaz' Regan and his wife. Failing to find any orange bitters to suit their tastes, they set about experimentation working from a 1939 recipe detailed in a book by Charles H. Baker, Jr.
After some trial and much error, Gaz encountered Mark Brown, CEO of The Sazerac Company at a festival and approached him about developing it commercially. After further work on the part of the Sazerac scientists, eventually a recipe was perfected that fit the bill, and Regan's Orange Bitters No. 6 was born.