On September 14, 1964, the Kellogg’s Company begins selling the Pop-Tart. The innovative portable-breakfast-treat-turned-anytime-snack would go on to sell billions annually and help redefine the breakfast food market.

It all started when one of Kellogg’s biggest competitors, Post Consumer Brands, trumpeted to the press that it had created an innovative new breakfast item: a shelf-stable, fruit-filled, handheld toaster pastry called “Country Squares.” It sounded like the ultimate grab-and-go convenience food. Anticipation ran high.

Problem was, their pastry wasn’t quite ready for market.

While Post dragged its feet on the actual product release, Kellogg’s—having heard the announcement—rushed to push out its own version. William Post (no relation to the company), a plant manager at the Michigan-based Hekman Biscuit Company, later described how a handful of Kellogg's execs showed up at his workplace out of the blue: They were waving two pieces of dough with some filling in it, saying, “We’d like to put that in a toaster.” They asked if he could develop and manufacture it on the quick.

Post and his team tried several versions of a new toastable pastry, roping in his own kids as taste testers. Six months after the Post Consumer Brands announcement, Kellogg’s beat its rival to market with a pastry it initially called..."Fruit Scones."

It didn't take long before marketing execs re-christened the pastry "Pop-Tarts," lending it some of the kitschy cachet of Pop Art, a buzzy art movement of the time made famous by Andy Warhol and his Campbell’s soup can paintings.

Pop-Tarts proved an instant hit. Shortly after a test release in Cleveland with four original flavors—Blueberry, Strawberry, Apple Currant and Brown Sugar Cinnamon—Kellogg’s completely sold out of its 45,000 test cases. And three months after its debut, sales proved so robust that Kellogg’s took out advertisements apologizing for not making enough of them, declaring, “Oops! We Goofed. (Will you excuse us, please) We ran out of Pop-Tarts.”

By 1967, Kellogg’s figured out a way to add frosting that wouldn’t melt in the toaster. Then came sprinkles, new flavors and a goofy mascot: Milton the Toaster. By the time Pop-Tarts turned 50 in 2014, dozens of flavors had been added and sales had grown every year consecutively for more than three decades. According to CNBC, consumers purchased more than 3 billion Pop-Tarts in 2022.

Though William Post is widely credited as the inventor of the Pop-Tart, Kellogg’s also credits "'Doc' Joe Thompson, and his kitchen crew’" as additional creators.