Vienna - Even the humble baseball cap he wore illustrated Niki Lauda's attitude to business and money -- the multi-millionaire never missed an opportunity to accumulate more.

Lauda, whose death on Monday has plunged world sport into mourning, was more than a sporting icon, he was also a hard-edged businessman who loved to win.

He wore a red baseball cap to partially disguise the terrible injuries suffered in a fiery crash in 1976 ... but also to turn a profit by renting out space on the hat to sponsors.

According to Trend magazine, the Austrian three-times Formula One world champion had amassed a fortune of between 150-400 million at the time of his death which he had astutely shared between assorted foundations with beneficial tax arrangements.

The wealthy lifestyle included a 10-million-euro Viennese villa, a 47-metre luxury yacht, a private long-haul jet which he flew himself, as well as a much-loved rural haven on the Balearic islands.

But the trappings of wealth seemed to mean little to a man who never spent wildly and was known for having a tight grip on the purse strings.

"I never bought a pullover or a pair of trousers until the old one was completely worn out," he told the German magazine Focus.

He actively encouraged the development of his reputation as a miser, and turned the image into a successful business brand. Recently he used it to promote a bank in a publicity campaign in which he boasted he had "nothing to give away."

He even joked that he would have sued his own mother for lost earnings because she gave birth to him too early -- because grand prix drivers earn so much more today than they did in his prime.

But beyond the jokes and money-grubbing reputation, Lauda was above all a skilled and visionary investor in the air transportation sector, his other passion outside of grand prix racing.

A pioneer of private charter flights, he set up Lauda Air in 1979 and sold it at a considerable profit to Austrian Airlines in 2002, 11 years after a crash which killed 223 on a flight from Bangkok to Vienna.

He launched a firm flying executive private jets, then embarked on a new adventure, creating his own low-cost airline, Niki, which he said started making money in its first year. He sold it for a comfortable margin to Air Berlin in 2011.

Six years later he bought it back for a bargain and with Austrian government backing when Air Berlin went under.

In January 2018 he played another ace, making a significant killing when he sold off 75 percent of the firm to Ryanair for 50 million euros.

He later sold off the remaining shares to Ryanair while holding on to the reins of the firm, renamed LaudaMotion and later, Lauda.

He believed he was an astute businessman, but denied he was ever really stingy.

"I believe I know how to spend money when the time is right," said the man who in 1996 flew a humanitarian aid plane to Kigali to deliver food to starving Rwandans devastated by war.