Savneet Singh, 29 ~ Gold Bullion International, President

Savneet Singh once dreamed of playing professional tennis. As a teenager, he even beat a young Andy Roddick at a tennis camp. But despite Mr. Singh's talent, he knew a professional sports career would be risky when it came to making a living.

Today, he is taking a different kind of risk: disrupting the gold business, an industry that hasn't changed much in 50 years. The company he co-founded, Gold Bullion International, is a digital platform where banks, businesses and individuals can buy, sell and store gold, ship it, insure it, and have it audited.

"What GBI does is make it transparent, electronic and extraordinarily liquid," said Mr. Singh, a former investment banker.

Angel-investors backed GBI started by signing up precious-metal dealers, vault owners and insurers as partners, and then spent 18 months pitching wealth-management firms. It didn't book a dime of revenue until Merrill Lynch and its army of financial advisers signed on in 2011, paving the way for banks, hedge funds and individuals to follow suit. Today, former banker Sally Krawcheck and former Securities and Exchange Commission Chairman Arthur Levitt sit on its advisory board.

Mr. Singh won't disclose GBI's backing or its revenue, but said the company has done billions of dollars in transactions in the past few years, and grew more than 20% last year.

"He's very smart," said Jesse Pujji, CEO of Ampush Media and a former adviser to GBI. "He can filter through the noise to find the signal, but the difference [between him and others] is he can turn around and get it done."

Mr. Singh is more modest: "The only genius in entrepreneurship is not giving up."