By Elizabeth Dilts Marshall

(Reuters) - Veteran Morgan Stanley <MS.N> executive Rich Portogallo, who was key in building the bank's prime-brokerage business, is retiring, according to an internal memo seen by Reuters on Wednesday.

Portogallo spent more than three decades at the Wall Street investment bank, and was well liked by colleagues for what one executive described as his tireless work ethic and calm, wise approach to stressful situations.

"There is no name more synonymous with the prime brokerage business at Morgan Stanley than Rich Portogallo," Ted Pick, the bank's chief of trading and investment banking, said in the memo.

Pick wrote that Portogallo's "humility and calm in the storm" will live on through the "enduring ... personal client relationships" he forged and that the bank now benefits from.

Portogallo started at Morgan Stanley's prime brokerage business in 1986, and over two decades made it the industry's go-to firm for hedge funds and big trading customers, the Wall Street Journal reported earlier on Wednesday.

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.

Portogallo most recently served as the bank's global head of institutional equities, clients and services.

He is expected to be out of the office by mid-March, according to the memo. The bank has not yet named a successor.

(Reporting by Bharath Manjesh in Bengaluru; Editing by Vinay Dwivedi and Jonathan Oatis)