Before he was denounced as a thief and cast out of the hedge fund industry, before he was a Goldman Sachs banker or a maths prodigy, Ke Xu was a little boy in Hubei province, who loved puzzles. His parents, junior government clerks, didn’t have much money, so Xu would scour the house to find old algebra and science textbooks. He spent hours with the series 100,000 Whys, children’s brainteasers with a Maoist flavour. The commune wants to build 40 tractors – how many wheels should it buy?

When Xu was 16, his head teacher identified him as a gifted student and recommended him for a scholarship at the Raffles Institution, in Singapore, a prestigious British-style boarding school with the Latin motto Auspicium melioris aevi (“Hope of a better age”). Xu master­ed English and cruised through his classes, if not the school’s extracurricular activities. Cricket was a mystery he could never solve.

After Raffles he moved to Britain to study mathematics at Cambridge University, eventually graduating third in a class of 250. Then, thousands of miles from home and with no enticing career ideas of his own, Xu took the advice of a profes­sor who had worked in the City of London’s financial district and applied to Goldman Sachs’ programme for graduates.

He joined the investment bank on the eve of the 2008 financial crisis and soon impressed his colleagues with his quick thinking and work ethic. The others on the credit derivatives pricing team were much like him, maths geeks from modest international backgrounds. Although Xu enjoyed the work, he didn’t find it challenging, and he didn’t fully embrace the Goldman Sachs gospel of money and power. On LinkedIn, he listed his job title as “dude” and one of his skills as “bread and butter making”.

Standing a little over five feet tall and wearing glasses, Xu was unimposing, but his confidence was ironclad. “I am born as a superstar stats trader [...] mathematical, commercial, hardworking, competitive, visionary and mentally tough,” he once boasted to his girlfriend, Mengyang, according to evidence from a lawsuit against him. “I have to live up to the great expectations that I have set for myself.”

Xu joined a Goldman Sachs graduate programme in the City of London, the British capital's financial district, after graduating from Cambridge University. Picture: EPA

By 2012, credit derivatives were out of fashion, and he decided it was time for something new. Then 28, Xu applied for jobs around the City and was offered a position by G-Research, part of a web of companies formerly known as the De Putron Fund Management Group, after its founder, Peter de Putron, a reclusive British hedge fund executive. G-Research’s website casts the company as a leader in quantitative research, with the slogan “Create today. Predict tomorrow”.