Investor Bill Hwang set off a storm in the stock market in March when his firm, Archegos Capital Management, and its banks, began liquidating huge positions in blue-chip companies, according to people familiar with the transactions. The sales sent individual stocks swooning and have left at least three banks with major damage. As a family office - a firm generally created to handle the investments of a single wealthy person and a small circle around them - Archegos was essentially unregulated.