Software engineer Zhang Yiming started out producing apps for sharing jokes before focusing on news aggregation. That pivot proved lucrative.

The 35-year-old founder of Bytedance Ltd. is worth about $13 billion, according to the Bloomberg Billionaires Index, making him China’s 9th-richest person and one of the fastest in modern times to amass a mega-fortune. The business, founded in 2012, has more than 1 billion active monthly users across eight mobile apps, including a news aggregator powered by artificial intelligence and a video-sharing platform.