Peter Karches, one of the key figures behind the success of Morgan Stanley Dean Witter's securities and investment banking business is to retire from the firm.

Karches, chief operating officer and president of the institutional securities and investment banking group, is stepping down after 25 years with the firm. John Mack, MSDW's president and chief operating officer, will take direct day-to-day responsibility for running the securities businesses in addition to his other responsibilities.