William “Bill” Post, who is credited with inventing the popular breakfast treat the Pop-Tart, has died at the age of 96.

According to his obituary, Post was the plant manager at Hekman Biscuit Co. (later Keebler Co.) in Grand Rapids, Michigan in 1964 when he was approached by executives with Kellogg’s. The executives asked for Post’s assistance in developing a new product.

Post’s invention debuted in 1964 with four flavors, strawberry, blueberry, brown sugar cinnamon, and apple currant. There are now more than 20 flavors. About 3 billion Pop-Tarts were sold in 2022, CNBC reports.

While he is credited with inventing the Pop-Tart, Post said he benefited from “an amazing team that developed Kellogg’s concept of a shelf-stable toaster pastry into a fine product that we could bring to market in the span of just four months.”

Post continued to work with Keebler and eventually moved to its corporate offices in Elmhurst, Ill. He retired at age 56 as a senior vice president. He later agreed to be a consultant for Kellogg’s, assisting the company for 20 years.

He and his wife, Florence, were married for 72 years before her death in 2020. The couple had four children and several grandchildren and great-grandchildren.