Morgan Stanley (NYSE:MS) announced Monday, that one of the co-heads of its core securities arm and a top deal-maker, Paul J. Taubman, will be retiring by the end of the year, following years of internal tussle  between two of its top executives.

After the retirement of Mr. Taubman, Colm Kelleher, co-head of the institutional securities division, will become the sole president of the unit and will report to the chairman and chief executive, James Gorman. Mr. Taubman’s retirement plans follow the decision of Mr. Gorman’s to elevate Mr. Kelleher.

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 “Paul is an outstanding banker and business leader who has made exceptional contributions, both to Morgan Stanley (NYSE:MS), and to our investment banking franchise during his highly distinguished 30-year career here,” Mr. Gorman said in an internal memorandum, reviewed by DealBook.

“On a personal level, Paul has been a valued strategic advisor to me on many critical issues we have faced these past few years”.

Mr. Taubman, regarded as the industry’s most prominent merger banker, has served Morgan Stanley(NYSE:MS) for 30 years. His role in brokering an invaluable contract with Mitsubishi UFJ Financial Group Inc (NYSE:MTU) of Japan was the sole reason that kept the firm afloat during the financial crisis. He was highly regarded as a top adviser to the media and telecom industries, with client lists including names such as Comcast Corporation (NASDAQ:CMCSA) and Time Warner Inc. (NYSE:TWX).

Mr. Taubman was made the co-president of the securities unit along with Mr. Kelleher, in January of 2010, and since then, both the executives have been involved in a power tussle over their shared leadership. The two have different backgrounds and styles: Mr. Taubman, a reserved investment banker, Mr. Kelleher an outspoken former head of global capital markets, with a taste for Cuban cigars. To ease the tensions, Mr. Kelleher was moved to London.

As per a person familiar with the matter, Mr. Kelleher’s rich experience in both banking and sales and trading helped him with the coveted position.  “His unique skill set and experience in global capital markets, as well as sales and trading make him ideally suited to lead the institutional securities businesses,” Mr. Gorman wrote in a separate internal memo.

Along with this news, Morgan Stanley (NYSE:MS) also announced that Mark Eichorn and Franck Petitgas had been named as the global co-heads of investment banking, reporting to Mr. Kelleher, while Jeff Holzschuh will take over as chairman of institutional securities, with a focus on maintaining key client relationships.