Benzinga and Yahoo Finance LLC may earn commission or revenue on some items through the links below. Billionaire hedge fund manager Bill Ackman described one of the most lucrative trades of his career during a recent appearance at The Citadel, calling a bet on a bankrupt shopping mall operator “the best investment” he ever made. At the time, GGP was the second-largest mall operator in the U.S. and burdened with $27 billion in debt, $15 billion of which was coming due within 18 months. The cab driver’s $50,000 investment in the stock, he said, turned into a $3 million retirement fund. The rescuing of mall operator General Growth remains a key milestone in Ackman’s career, with the company being acquired by Brookfield Property Partners (NASDAQ:BPYPN) for $9 billion in 2018.