Ji Xu played a key role in building the world’s largest payment platform, which can support more than a billion transactions a day. It’s a boon to commerce, but more important, it enables anyone—especially people without access to traditional banks—to use financial services over the internet.

Originally developed to make payments on Alibaba’s online shopping sites easier and more reliable, Alipay has become a ubiquitous electronic payment app in Chinese e-commerce and brick-and-mortar stores alike. It has 520 million users, who see cash as a thing of the past: whether grocery shopping, paying utility bills, or buying movie tickets, they simply pull out a smartphone and use Alipay to scan a payment code.

As its business grew, Alipay was confronted with two challenges. First of all, it needed to increase the number of transactions it could handle. In addition, it needed to manage a growing variety of funding options. People had started linking all sorts of funds—credit cards, debit cards, electronic cash gifts, and investment portfolios—with Alipay to pay for things, and sometimes one purchase was made using multiple types of funds.

As the chief architect of Alipay’s core payment platform, Xu led a team that increased the system’s capacity from 10 million to 100 million transactions a day, and eventually to one billion. The new system can use servers located anywhere without causing delays during peak hours, which is crucial because the servers consume so much power that no single location can support enough of them to meet the system’s requirements.

The increase in Alipay’s transaction capacity also made it possible to offer online financial services to anyone, regardless of income level. One popular feature of the app lets users invest their leftover cash from online spending in a fund and earn interest at higher rates than they could at a bank.

Growing up near Hangzhou, where the Alipay team is based, Xu was not interested in taking exams. He spent about two years in a computer science program in college before leaving to look for a job, and he joined Alipay at 23. “I wanted to learn technologies,” he recalls. While on the job, he caught up on programming knowledge through online courses.

—Yiting Sun