When you grow up eating Mazola, you tend to think that margarine was always made of corn oil. That's far from the truth, as many different kinds of fats have been used to make the butter substitute. The only requirement was that it had to be cheaper than butter; otherwise people would just buy butter. That included whale oil, which was widely used for fuel before the rise of the American petroleum industry.
Margarine was invented in 1869, just as whale oil was on the verge of falling out of use as a fuel. To simulate butter, margarine must contain some kind of fat. That might come from a variety of vegetable oils—as in most margarines today—or beef fat. But in the first half of the 20th century, since whale oil was “no longer needed for illumination” and a “large amount became available,” as one researcher wrote in the 1960s, most of the world’s supply was being whipped into a spreadable butter substitute.
Read up on the history of whale oil margarine, which was so popular that it led to the formation of one of the world's largest corporations, at Atlas Obscura.
(Image credit: KingaNBM)