Mr. Blake and his brother sold Friendly to the Hershey Foods Corporation in 1979 for about $164 million (nearly $580 million in today’s dollars). The Tennessee Restaurant Company bought the chain from Hershey in 1988 and officially changed the name to Friendly’s the next year. Friendly’s is now owned by an affiliate of Sun Capital Partners, a private equity firm that bought it for $337 million in 2007.

Friendly’s has struggled in recent years because of the 2008 recession, as well as changes in the restaurant industry and diners’ preferences. It filed for bankruptcy protection in 2011 and closed about a hundred stores.

John Maguire, a Massachusetts native and former Panera Bread executive who became the chief executive in 2012, told The Boston Globe’s magazine the next year that part of his strategy for reviving Friendly’s was to emphasize nostalgia. Many of the remaining 171 Friendly’s restaurants now display photographs of the original store and pictures of the Blake brothers wearing bow ties, genial emblems of a bygone age. (Mr. Maguire stepped down in 2018, when George Michel, the former chief executive of Boston Market, took over.)

A customer might even have run into one of Friendly’s actual founders in a restaurant: Curtis Blake was especially fond of Friendly’s hamburgers and Forbidden Chocolate ice cream. The last time he dined at a Friendly’s was during the winter of 2017, in Port St. Lucie, Fla.

Curtis Livingston Blake was born on April 15, 1917, in Springfield, to Herbert Prestley and Ethel (Stewart) Blake. His father worked for the Standard Electric Time Company, which made electric clocks; his mother was a homemaker and car enthusiast who encouraged her sons’ lifelong interest in collecting classic automobiles.

Mr. Blake graduated from Technical High School and started Friendly with his brother before serving in the Army Air Forces in England during World War II.