Reed, 61, said in a conference call that it all made perfect sense. The merger is working; he, Weill and Citi’s tough-minded board all agreed it was time for a single chief. Reed, a technovisionary who helped bring the world ATMs, said he is ready to retire. Contradicting some of the handicapping of two years ago, Citi insiders indicate that the megadeal may in fact have been a sort of exit strategy for Reed after a tumultuous career. The $250 million in Citigroup stock he controls makes the exit a pleasant one. And so, perhaps, does the public commitment of Weill–who is 66–to hand off the CEO job in two years. Now Wall Street is buzzing about who will next run a company that earned nearly $10 billion last year, more than Microsoft and second only to GE. Former Treasury secretary Robert Rubin, who joined Citigroup in a vaguely defined but nonexecutive leadership role in October, reiterated that he isn’t interested in the job. That turned the spotlight on the next tier of Citi execs–where there’s talent but probably not the star quality needed to run a company that operates in 100 countries around the world.

Weill might solve the problem with a deal. Analysts expect him to keep up a steady pace of acquisitions, and Citigroup is so big that few financial firms are beyond its reach. It is, among other things, the world leader in credit cards, and one Wall Street scenario has Weill going after American Express, which would allow him to bring AMEX’s widely respected Kenneth Chenault on board as his heir. Citicorp and AMEX actually considered a merger in 1997.

But there’s also speculation that Weill might turn to his former right-hand man. When Weill first proposed merging Traveler’s with Citicorp, one of the assets he brought to the deal was a potential future CEO: Jamie Dimon, then 41. But when Dimon and Reed disagreed on how the two companies would combine some overseas operations, Weill stood back as Reed forced Dimon out. Officially, Citigroup declines to comment on Dimon’s possible return; off the record, several insiders are skeptical. Weill did have a rather public lunch with Dimon at the Four Seasons in December. Whether it was just for old time’s sake or a recruiting session will soon become clear.