Until recently, Bill Hwang sat atop one of the biggest — and perhaps least known — fortunes on Wall Street. Then his luck ran out.Mr. Hwang, a 57-year-old veteran investor, managed $10 billion through his private investment firm, Archegos Capital Management. He borrowed billions of dollars from Wall Street banks to build enormous positions in a few American and Chinese stocks. By mid-March, Mr. Hwang was the financial force behind $20 billion in shares of ViacomCBS, effectively making him the media company’s single largest institutional shareholder. But few knew about his total exposure, since the shares were mostly held through complex financial …
