One of my favorite "rich guys are smart until they're not" stories involves the Hunt Brothers.
Convinced that fiat currency was on the way out (history may not repeat, but it does rhyme!) they decided to corner the silver market. Which worked great! Using the inherited wealth of their father (a billionaire), along with aggressive margin positions, they managed to acquire a decent portion of the world's supply of silver ... I think it was over 1/4 ... driving the price up nearly eightfold in a year.
Unfortunately, it didn't last. And fiat currency managed to stick around. The price started to collapse, and the Hunts were wiped out. Contrary to the old saying, the bankruptcy happened quickly, and all at once.