Gates, 62, would have a net worth of more than US$150b if he'd held onto assets that he's given away, largely to the Bill & Melinda Gates Foundation. He has given away almost 700 million Microsoft shares and US$2.9b of cash and other assets since 1996, according to an analysis of his publicly disclosed giving.
Bezos also controls closely held space exploration business Blue Origin and The Washington Post.
While Bezos might be considered the richest man in recent history, his wealth doesn't yet match the fortunes accrued by some of the great historical emperors.
A 2015 study by Time magazine's Jacob Davidson put African king Musa Keita, the ruler of the Mali empire between 1280 and 1377, as the richest person of all time.
Jacobsen wrote that the extent of his wealth was incomprehensible.
"There's really no way to put an accurate number on his wealth," he told the Business Insider.
A distant second on his list was Augustus Caesar, whose wealth he estimated at US$4.6 trillion when adjusted for the modern context.
Other figures to make the list included Chinese Emperor Shenzong, who commanded as much as 30 per cent of the global GDP at the time, Josef Stalin, who was in control of 9.6 per cent of the global GDP as leader of the Soviet Union and oil magnate John D Rockefeller, whose wealth was estimated at US$344b at its peak.
While historical comparisons are always difficult, an enormous concentration of wealth with one person is nothing new.
