Kellner, 56, was among the five, including the pilot, killed on Saturday in the crash near Knik Glacier northeast of Anchorage, Alaska State Troopers said. One survivor was taken to hospital, they said, adding the group had been on a heli-ski tour.

Kellner, who avoided public attention, was featured in one PPF annual report on a snowboard. A spokeswoman for the exclusive Tordrillo Mountain Lodge, where the crash victims were staying, said Kellner had been a frequent guest since 2012.

Petr Kellner

Kellner was a towering figure in the Czech Republic's post-communist era, amassing wealth estimated at $17.5 billion according to Forbes. He was the world's 68th richest person on Forbes' 2020 list, tied with media giant Rupert Murdoch and his family.

PPF in a statement expressed "deepest grief" at the death of its founder and 98.9% shareholder.

Ladislav Bartonicek, a 30-year PPF veteran who owns just over a 0.5% stake, will take over management duties, the company said.

PPF's third shareholder, Jean-Pascal Duvieusart, also with just over 0.5%, said the company would continue building and keeping with Kellner's vision.

"Petr was somebody who was truly extraordinary in terms of energy, in terms of creativity, in terms of a drive to build new things," Duvieusart said in a telephone interview.