A decade after the financial crisis, The Wall Street Journal has checked in on dozens of the bankers, government officials chief executives, hedge-fund managers and others who left a mark on that period to find out what they are doing now. Today, we spotlight former Morgan Stanley CEO John Mack.

When John Mack stepped down as Morgan Stanley’s chief in 2010, his successor, James Gorman, offered him an office a few doors down from his own on the 41st floor of the bank’s Times Square headquarters. “Trust me,” Mr. Mack says...