One of Morgan Stanley's top foreign exchange executives, Stephen Mettler, plans to retire from the company, according to an internal memorandum sent to employees.

In the memo reviewed by Dow Jones Newswires, the firm said Mettler, its global head of macro who has overseen the interest rates and foreign exchange as well as the rates and currency portion of its emerging-markets businesses, helped drive Morgan Stanley's recent market share gains in those areas.