(FORTUNE Small Business) – Whom can we blame for our nation's descent into gluttony? Pin at least some of it on brothers-in-law and business partners Burt Baskin and Irv Robbins. The two harbored a most innocent ambition in the bustling postwar years of the late 1940s. All they wanted was to satisfy the country's craving for sweets. Their kitchen collaboration yielded a trove of sinful ice-cream concoctions, among them the infamous Rocky Road. On that nutty idea was built the biggest chain of ice-cream parlors in the world.

Today, Baskin-Robbins shops are a beloved part of Americana. Millions of people can recall the delicious agony of trying to choose a flavor from the colorful tubs of ice cream crowding the freezer. Burt, who died in 1967, and Irv helped pioneer the concept of extravagant excess--a cumulative 1,000 flavors and counting--and they were among the first to franchise. Baskin-Robbins now has 5,000 stores in more than 50 countries.

Oddly--or maybe fittingly--this sweet saga started in the Depression. As a teen in Tacoma, Irv Robbins managed a tiny ice-cream shop that was typical of the era's drugstore-counter and ice-cream-parlor traditions. Even then, he rebelled against the drudgery of vanilla, chocolate, and strawberry. He mixed fresh fruits and candies into his product and gave the concoctions fanciful names.

World War II postponed Irv's dream, but as soon as he was discharged from the Army in 1945, he invested $6,000 in a parlor in Glendale, Calif. Within three years, Irv had persuaded his brother-in-law, Burt Baskin, to join him. The two men flipped a coin to determine whose name would go first, and the latecomer got top billing.

Baskin-Robbins banked on an everchanging smorgasbord of flavors. Stores advertised the odd number 31 to suggest something new for each day of the month. Many of the flavors became classics, among them Pralines 'n Cream and Jamoca Almond Fudge. But there were a few bombs too. Goody Goody Gumdrop turned out to be bad (customers chipped teeth on the frozen gumdrops). And as for Statutory Grape...that one never made it to market.

Managing parlors proved to be exhausting for Burt and Irv--and it distracted them from their first love, formulating new flavors. They franchised the business, which allowed it to grow rapidly nationwide. Their strategy was one that their former malt-machine salesman, Ray Kroc, later applied to his fast-food restaurant chain, McDonald's. In 1967, the duo sold their business for an undisclosed amount to United Fruit, which was later acquired by Britain's Allied Domecq.

Baskin-Robbins grew explosively in the 1970s, opening a store just about every other day for a while. But the 1980s weren't kind to Baskin-Robbins. The sanitary white stores began to look more rundown than retro. Ben & Jerry's, Haagen-Dazs, and regional upstarts began devouring the chain's business with a new superfat ice cream and a hip aesthetic. Perhaps the unkindest cut of all came from Irv's only son, John, a healthful-living advocate who eschewed high-fat foods, especially his dad's product.

Baskin-Robbins is trying to turn things around now with a multimillion-dollar renovation of its parlors. Maybe softer lights and comfy furniture will bring back fans. But its brightest hopes may lay overseas, where it is still an icon of Americana in such places as Japan and Korea. Green Tea ice cream, anyone?