Currently serving as a senior advisor at Morgan Stanley, John Mack is an American businessman with an estimated net worth of $100 million in 2012. John Mack has also served as the company's chairman and CEO until his retirement in 2009. Morgan Stanley is a brokerage firm and investment bank which is currently based in New York City. After his retirement, he was succeeded by James P. Gorman, his former co-president.

After graduating from Duke University, John Mack worked at several firms in Wall Street before he settled at Morgan Stanley as a salesman. He spent thirty years of his life at Morgan Stanley and his responsibilities were gradually increased. From 1985 through 1992, he served as the head of Worldwide Taxable Fixed Income Division. Two years later, he became a part of the Board of Directors. In June 1993, he became the President of  Morgan Stanley. Later on, when the world's two leading financial institutions, Dean Witter and Morgan Stanley, merged, John Mack became the Director, Chief Operating Officer and President of Morgan Stanley Dean Witter & Co.. However, his power dispute with Phil Purcell led him to leave the company in 2001. He returned in 2005, and he replaced Purcell as the Chairman of the Board and Chief Executive Officer.