In November 2012, Morgan Stanley announced that Mr. Kelleher would be the sole head of institutional securities, and that Mr. Taubman was leaving. Mr. Taubman could have stayed on as a senior deal maker reporting directly to the firm’s chief executive, James P. Gorman, but it was clear his upward trajectory at the firm was over. “There was panic” at Morgan Stanley, one banker there told me. “Everyone was afraid the deal business would collapse.”

Mr. Taubman had no immediate plans. When Barry M. Wolf, executive partner at Weil, Gotshal, called to offer him office space, Mr. Taubman said he liked the idea of having an office to go to and a place to reconnect with clients. (He and his wife have a 2-year-old son at home, which is now an apartment on Central Park West that he bought from the comedian Robin Williams in 2000.) “The best advice I got was take some time and don’t rush into anything,” Mr. Taubman said.

But after just five relatively low-key months — he spent more time with his wife and son, got into shape at the gym and became board president of the volunteer group New York Cares — Mr. Taubman received an email from the head of corporate development at Verizon. Mr. Taubman had worked for Verizon for many years, including on the issue of what to do about the half of Verizon Wireless that Vodafone owned. Mr. Taubman met with Verizon’s board and was soon enmeshed in the deal as a top adviser. Then, in October, he received a call from Comcast asking if he could help on the Time Warner Cable deal.

There turned out to be a silver lining for Morgan Stanley, because Mr. Taubman is working alongside his former colleagues in both deals. Morgan Stanley represented Verizon and is now working for Time Warner Cable. Morgan Stanley currently ranks No. 1 in the merger and acquisition league tables.

Mr. Taubman is close to Comcast’s chief executive, Brian L. Roberts. “Paul is one of the smartest and most creative individuals I’ve ever worked with,” Mr. Roberts told me this week. “His capacity to think out of the box and to make things happen is almost unparalleled. He’s been an invaluable counselor to Comcast and to me for over 20 years. And it’s always a genuine pleasure to work with him.”

Jimmy Lee, the prodigious deal maker at JPMorgan Chase, has worked closely with Mr. Taubman for decades, including on General Motors’ initial public offering in 2010. He is also advising Comcast on the Time Warner Cable deal. “There are only a few bankers who command the allegiance and respect from chief executives and board chairmen that Paul does,” Mr. Lee said. “And he’s a closer. His deals get done. On top of all that, he’s got this wonderful sensibility. I always feel we’ve come together and are working for the client, and that’s what matters. There’s never been one iota of Wall Street rivalry between Paul and me. That’s a recipe for someone who can land two of the biggest deals right out of the box. He was perfectly suited to starting his own firm.”