Subway says it now has more than 40,000 locations worldwide, topping McDonald's and Starbucks.
“We didn't make a profit for 15 years,” Buck told The Wall Street Journal in 2014.
Asked if he ever thought the chain would grow so big, he told the newspaper, “Well, I always thought we’d get bigger and bigger, but I really didn’t have a certain number in mind.”
As a physicist, Buck was hired by General Electric in 1957 at a laboratory in Schenectady, New York, and worked on atomic power plants for U.S. Navy submarines and ships. He later worked for United Nuclear in White Plains, New York, and Nuclear Energy Services in Danbury, where he made his home, according to an obituary prepared by his family.
He also pursued philanthropy, making significant donations to many organizations including the Smithsonian Institution, to which he gave a 23-carat ruby named after his late second wife, Carmen Lucia Buck, in 2004.