Other top executives include Heidi Miller, the chief executive of treasury and security services at JPMorgan Chase; Amy Woods Brinkley, the chief risk officer at Bank of America; and Erin Callan, chief financial officer of Lehman Brothers.

But with Ms. Cruz no longer a candidate to run Morgan Stanley, the top executive ranks at the big Wall Street firms remain largely devoid of women seen with a viable chance of becoming chief executive anytime soon. Women have also not been considered for recently created openings at Citigroup and Merrill Lynch.

Firing a top executive is never a pleasurable experience, as any chief executive will say. But in the case of Mr. Mack, who for Ms. Cruz has been a mentor, champion as well as her most stubborn defender against her many enemies, the decision to force her retirement was undoubtedly wrenching.

On Thursday night, just hours after the news of Ms. Cruz’s departure had become public, he presided over a cocktail party for former Morgan Stanley executives now in the hedge fund industry at the Asia Society. “It’s been a rough day,” he said to the audience, according to a person who was there.

In 1982, Mr. Mack was a rising star in the firm’s fixed income business — at the time a relative backwater for Morgan Stanley compared with its blue-chip underwriting and advisory business. And while women investment bankers could occasionally be found, women traders were a rarity.

With her brash personality, Ms. Cruz took quickly to the rough and tumble culture of Morgan’s trading business — soon securing the nickname Cruz missile. She carved out a niche as foreign exchange trader with an expertise in derivatives and in 1993, Mr. Mack, who had become president of the firm, made her co-head of the firm’s foreign exchange business and one of the top women executives at the firm.

In 2000, Mr. Mack promoted her again to a more substantial post — running the bank’s fixed income business, one of the biggest profit generators at Morgan Stanley. While Ms. Cruz had done well as a foreign exchange trader, running fixed income was a larger challenge and Mr. Mack’s elevation of her over male candidates raised eyebrows, according to executives who worked with her at the time.