Harold Butler, 77, the founder of the Denny's restaurant chain, died of a heart attack July 9 in the Mexican resort city of La Paz, where he had lived the last two years.

He owned the Puerto Mexia resort development in the Gulf of California port city.

Mr. Butler, who founded or headed several other chains as well as Denny's, was considered a pioneer of the modern fast-food concept.

He created Denny's in 1953 from his tiny Danny's Donuts in Lakewood, Calif. The 900-square-foot establishment sold fresh doughnuts stuffed with jam (not jelly) and high-quality coffee, then a rarity. When he opened a second shop in nearby Garden Grove, he added a grill and offered hamburgers as well as doughnuts. The chain grew into Denny's, a name Mr. Butler simply made up.

Denny's is now a subsidiary of the Spartanburg, S.C.-based Advantica Restaurant Group. It has 1,600 fully owned or franchised restaurants nationwide.

Mr. Butler's concept for Denny's, which he and his competitors mimicked repeatedly over the decades, called for low prices, high volume, uniform menus and fast service.

In 1969, he attempted to expand Denny's into the Las Vegas hotel-casino industry by purchasing Parvin-Dohrmann Co., then owner of Caesars Palace and other complexes. The Securities and Exchange Commission accused Mr. Butler of privately making a better offer to some Parvin-Dohrmann shareholders that was not available to all public shareholders. The purchase deal fell through.

As a result, Mr. Butler stepped down as chairman and sold his Denny's stock, once worth $80 million, for $3 million in 1971. At that time, Denny's had some 800 restaurants.