Subway co-founder Peter Buck, who turned his initial investment of $1,000 into more than a billion dollars, died Thursday at the age of 90, the company confirmed. With more than 40,000 locations worldwide, Subway today is now the world’s largest submarine sandwich chain. Buck, the company’s last surviving founder, left a net worth of $1.7 billion, according to Forbes. “We are deeply saddened by the passing of one of Subway’s founders, Dr. Peter Buck. He was a shining example of a dedicated, hands-on leader, and an integral member of the Subway family,” John Chidsey, CEO of Subway, said in a statement. In 1965, Buck gave his family friend, Fred DeLuca, the idea to open a submarine sandwich shop to help the then-college freshman make money for college. Buck, who was a nuclear physicist, provided an initial investment of $1,000, and “Pete’s Super Submarines” opened in Bridgeport, Connecticut. By 1974, the two owned and operated 16 shops in Connecticut and then began franchising them. According to the food service research and consultant firm Technomic, sales at Subway’s US locations have fallen in recent years. Amid competition from other fast-food companies, system-wide sales at Subway’s US locations have fallen to $8.3 billion in 2020, down from $12.3 billion in 2013, its best year of the past 15, according to Technomic’s analysis. When Subway first rose to prominence in the 1970s and 80s, it “owned” customization, said Robert Byrne, director of consumer and industry insights at Technomic, meaning customers could choose what they want in real time. Now, customers can build their own burritos, salads, sandwiches or bowls, making for fierce competition in the space. As more restaurants offer custom options, “we want to continue to … dominate that space,” said Chidsey earlier this year. Subway revamped its menu with new recipes and toppings in July, which helped the company increase its sales in August 2021. Buck’s fellow Subway founder DeLuca died in 2015 at age 67. Buck was born in 1930 in South Portland, Maine. He graduated from Bowdoin College in 1952 and earned his master’s and doctoral degrees in physics from Columbia University. His philanthropic efforts were managed by The Peter and Carmen Lucia Buck Foundation, which he founded with his late wife in 1999.