He searched for oil in the badlands of Somalia and fueled a stock market boom in Mongolia. He sued the world’s smallest republic, far out in the Pacific, for a chunk of what it is worth.

Now, he is betting on North Korea.

James Passin, a hedge fund manager at Firebird Management, believes the nuclear-armed country sits on as much as a billion barrels of crude — enough to make it as big a producer as Oklahoma. If the oil exists, he wants to help unlock it.

“You have a country with 25 million people — young, highly disciplined, literate — and a strong military-industrial complex,” he said in an interview. “It’s possible that the early investors will be rewarded with potential for massive appreciation.”

The risks of sinking cash — even just $7 million or so of Firebird’s $700 million in assets — into a neo-Stalinist state with labor camps and virtually no private property are obvious. The geopolitical volatility was on full display last week, as North Korea claimed that it had tested a hydrogen bomb. And Mr. Passin is treading on murky investment territory, given the American sanctions against the country.