Whisky is generally used to refer to the whiskies distilled in Scotland, Islay, Japan, India or Canada, while whiskey is used in the United States and Ireland. In the late Victorian era, the Irish whiskey was the finest in the world and the whiskey of Dublin was recognized as one of the best. In order to differentiate the one of Dublin from the other whiskeys, the Dublin distilleries used the spelling whiskey, being imitated later by other distilleries. The last Irish whiskey was Paddy, who adopted the ‘e’ in 1966.
Even though in 1968 the Bureau of Alcohol, Tobacco and Firearms specified whisky as the right way to name the beverage in the United States, most US producers still use historical spelling. But with any rule there are a few exceptions. For example, George Dickel or Maker′s Mark Tennessee Whisky are spelled without the “e.”