After a long hiatus, George Soros has returned to trading, lured by opportunities to profit from what he sees as coming economic troubles.

Worried about the outlook for the global economy and concerned that large market shifts may be at hand, the billionaire hedge-fund founder and philanthropist recently directed a series of big, bearish investments, according to people close to the matter.

Soros Fund Management LLC, which manages $30 billion for Mr. Soros and his family, sold stocks and bought gold and shares of gold miners, anticipating weakness in various markets. Investors often view gold as a haven during times of turmoil.

The moves are a significant shift for Mr. Soros, who earned fame with a bet against the British pound in 1992, a trade that led to $1 billion of profits. In recent years, the 85-year-old billionaire has focused on public policy and philanthropy. He is also a large contributor to the super PAC backing presumptive Democratic nominee Hillary Clinton and has donated to other groups supporting Democrats.

Mr. Soros has always closely monitored his firm’s investments. In the past, some senior executives bristled at how he sometimes inserted himself into the firm’s operations, usually after the fund suffered losses, according to people familiar with the matter. But in recent years, he hasn’t done much investing of his own. That changed earlier this year when Mr. Soros began spending more time in the office directing trades. He has also been in more frequent contact with the executives, the people said.