It is most likely that the custom of eating hot dogs was introduced to North America by German immigrants. The popularity of the food surged with the waves of immigrant workers that arrived in the USA starting in the late 19th century, and liked food that was easy to eat and cheap.
According to some, the term “hot dog” was coined in during a cold April day 1901 at the New York Polo Grounds. Vendors allegedly shouted “They’re red hot! Get your dachshund sausages while they’re hot!”
Allegedly, cartoonist Tad Dorgan observed this and drew barking dachshund sausages rolled neatly in buns. Unsure of how to spell “dachshund”, he simply wrote “hot dog”. However, the existence of such a cartoon has never been proven, and the story is likely not true since we have evidence the word first appeared prior to 1901.
Others point to 1890s college magazines, where the term appears associated to “dog wagons” that sold sausages at the dorms. The term was satirical in nature, and alluded to the origin and quality of the meat.
Yet another theory links the origin of the word to the mentioned German immigrants, who called frankfurter sausages “little dog” or “dachshund” (they were thin and long, just like that dog breed). In fact, “dog” was often used as a slang term for a sausage in the late 19th century.
The two other terms for the sausages, “frankfurter” and “wiener” have sparked a debate as to whether they originate from Frankfurt-am-Main, Germany or Vienna, Austria.
It is also interesting that the expression “hot dog” was used on the turn of the 20th century, and meant someone was particularly skilled or excellent, with connotations of showing off. It is unknown whether there is any relationship between this expression and the popular food.