Russians laid flowers in front of the Wagner Group's private military company headquarters in St. Petersburg on Thursday following news of Yevgeny Prigozhin's presumed death.
Prigozhin and top officers of his Wagner company were aboard a plane that crashed on Wednesday night.
The incident was widely seen as an assassination.
It comes two months after they staged a mutiny that dented President Vladimir Putin’s authority.
Rescuers found all 10 bodies and Russian media cited sources in Prigozhin’s Wagner company who confirmed his death.
"It feels like losing a father," a man, who said he'd fought with Wagner in Luhansk, Ukraine, told The Associated Press.
Prigozhin’s forces fought some of the fiercest battles against Ukraine over the last 18 months but pulled back from the frontline after capturing the eastern city of Bakhmut in late May.