Yevgeny Prigozhin, who led a failed mutiny against Vladimir Putin, was on a plane that crashed in western Russia, say aviation officials.
Authorities say all 10 people on board were killed after the private aircraft came down near the village of Kuzhenkino.
They also say the passengers included Prigozhin, who is the head of mercenary group Wagner, and his right-hand man Dmitry Utkin.
Russian authorities have launched an investigation into the cause of the crash, amid heavy speculation.
Prigozhin kept a low public profile since he led his mutiny in June, which lasted only 24 hours.
He last appeared in a video earlier this week which was said to have been filmed in an unspecified location in Africa.
The Wagner mercenary group was founded in 2014 and was highly active in the Ukraine war until the mutiny.