By 1978, Ludwig was estimated to be worth around $12 billion ($9.9bn) in today's money, making him America's richest person, yet he remained almost unknown in the US. The invisible tycoon lived in a large apartment in Midtown Manhattan but even his closest neighbours had no idea who he was. Ludwig died at home at the age of 95 in 1992; Forbes estimated his wealth to be $1.2 billion at this time, the equivalent of $2.2 billion (£1.8bn) in today's money.