At the time, millions of Chinese were opening stock accounts with an enthusiasm that proved long-lasting and transformative. Between Shanghai and a second exchange in Shenzhen, the market grew from a capitalization of $61 billion in 1993 to $10 trillion by the summer of 2015. Unlike in the United States, where institutional investors dominate the market, China’s 200 million mom-and-pop investors make roughly 85 percent of all trades. According to a survey by the State Street Center for Applied Research, 81 percent of these trade at least once a month. But less-experienced individual investors are easily swayed by rumors and operate with a poor understanding of market fundamentals, making them easy prey for more systematic and sophisticated traders. “All these small individual investors are called ‘chives’ in the market,” says Hong Yan, a finance professor at the Shanghai Advanced Institute of Finance. “They get cut over and over again, but they come back every time, like little weeds.”

In his early days, Xu worked from the Galaxy Securities trading hall on South Liberation Road in Ningbo. Stock prices were written in chalk on blackboards, and arbitrary rule changes affecting stock issuance and corporate disclosure constantly jostled an already unpredictable market. In 1992, the Shanghai index grew by 167 percent — then tumbled roughly 75 percent between April 1993 and July 1994. The fact that China Galaxy Securities was a state-owned enterprise offered little protection; as Xu cut his teeth, the traders around him won and lost fortunes almost overnight.

On an overcast Monday morning last December, I visited Galaxy. The building itself had hardly changed from the days when Xu first set foot inside. Located beside a pharmacy that glowed with blue lights, the eight-story structure seemed on the verge of physical collapse. A wide concrete staircase, littered with cigarette butts and sun­flower seeds, led up to the main trading hall on the second floor, which, by 9 a.m., was packed with haggard-looking investors. Directly opposite the trading board, hung above a small statue of a golden bull, was a red banner urging traders to “stay away from illegal securities activities.”

The heady tumult of those early days in China’s stock market shaped what would become Xu’s signature style: Buy quickly, sell quickly and always go big. It was the familiar ethos of day trading, but taken to the extreme within a Wild West market in which information was scarce, unreliable or nonexistent. Xu won renown so quickly that by 1995, at 19, he was rumored to be the subject of a heated dispute between two powerful Shanghai gangsters. Having seen the lucrative potential of the market, and the exceptional returns of the young trader, both men wanted Xu as their own personal investor. Several sources told me that the dispute was eventually settled by a leader from one of China’s infamous triad gangs — and that, improbably, the episode later became the inspiration for a series of Hong Kong gangland movies about stock-market geniuses.

As Xu’s fame grew, so did his network. By the late 1990s, he became the unofficial captain of a group popularly known as the Ningbo Death Squad. The squad made its reputation by manipulating cheap, relatively unknown stocks, which in the Chinese market are not allowed to rise or fall more than 10 percent in a single trading day. To game the system, the squad devised a strategy: Out of nowhere, it would place a gigantic order for a chosen stock. Other traders, seeing the sudden upward movement in price, would flood in, pushing the stock toward its daily 10-percent limit. Once the stock hit the limit on the first day, the momentum became self-perpetuating. Eager traders rushed to buy the stock as soon as the market opened the next day, propelling it toward the 10-percent limit once again. The movement generated its own publicity and easy profits. After a few days, the squad would sell out, and the stock would tumble back to a lower price as other traders followed. In the American context, this tactic was reminiscent of present-day schemes in “penny stocks,” but with much higher stakes, and playing out in a regulatory environment that mirrored the early days of the United States market. One Chinese day trader I talked to spoke in reverent tones about the turn-of-the-century American stock picker Jesse Livermore, who made and lost several multimillion-dollar fortunes before killing himself in 1940 at 63.

As the squad gained notoriety, other traders began to monitor the buy orders coming from the Galaxy trading hall — any stock they picked was guaranteed to attract attention, and a corresponding surge in buy orders. Profit was almost unavoidable.