Billionaire investor Bill Ackman has publicly recommended buying Fannie Mae and Freddie Mac stocks, a rare move for him. He has held these positions for over a decade, with recent gains reportedly doubling his net worth and making them his most profitable holdings. These government-backed entities, in conservatorship since 2008, buy mortgages from banks, package them, and sell them to investors, backing about 70% of U.S. home loans. Since 2019, they have been allowed to retain earnings, leading to significant profitability.