Robert Paxton McCulloch was already a multi-millionaire by the time he turned 18.

But inheriting part of his grandfather’s fortune in 1925 didn’t blunt his ambition or work ethic. Driven by a compulsion to invent, after graduating from Stanford University he started a company that created supercharged car engines.

While he was still a young man McCulloch sold the business for $1m. It was the first chapter in a lucrative career that would take him from the Midwest to California, where he had successful ventures making chainsaws and boat engines.

“He was a genius,” says his grandson Michael. “He was astute at building and invention; he designed engines - that was his forte.

“He was a little on the eccentric side, but extremely nice. I only ever saw a very gentle person.”