(Adds quote from memo, context on prime brokerage business, background on Ehrlich, byline)
By Lawrence Delevingne
NEW YORK, Oct 7 (Reuters) - Alex Ehrlich, co-head of the prime brokerage business at Morgan Stanley, plans to retire at the end of 2019, according to an internal memo seen by Reuters and confirmed by a spokesman.
Ben Walker, who also co-heads the business, will become the sole chief of the unit, the Oct. 7 memo said.
Ehrlich joined Morgan Stanley in 2009 after roles at UBS AG and Goldman Sachs in a career spanning 40 years.
Ehrlich and Walker did not immediately respond to requests for comment.
The memo said Ehrlich "played a critical role" in the management Morgan Stanley's prime brokerage business and has been "instrumental in overseeing the growth and success" of listed derivatives and fund administration.
"He has been a champion of diversity and has had a huge impact on our culture, our clients and the development of our people," the memo said.
Morgan Stanley is usually at or near the top of prime brokerage and equities trading rankings. Prime brokers provide services to hedge funds and other large investors, including help with trading and raising money. (Reporting by Lawrence Delevingne; Editing by Richard Chang)