A former convict-turned-restaurateur, Yevgeny Prigozhin’s humble origins gave way to an astonishing, if unlikely, ascent.

The head of the Wagner Group of mercenaries has reportedly been killed in a plane crash, putting Russia’s internal security and the future of the controversial military unit in jeopardy.

Fighting alongside Malian soldiers, Wagner mercenaries have massacred civilians and burned their villages in northern Mali, ...