Alibaba Group founder Jack Ma, who helped launch China’s online retailing boom, stepped down as chairman of the world’s biggest e-commerce company Tuesday at a time when its fast-changing industry faces uncertainty amid a U.S.-Chinese tariff war.

Ma, one of China’s wealthiest and best-known entrepreneurs, gave up his post on his 55th birthday as part of a succession announced a year ago. He will stay on as a member of the Alibaba Partnership, a 36-member group with the right to nominate a majority of the company’s board of directors.

Ma, a former English teacher, founded Alibaba in 1999 to connect Chinese exporters to American retailers.