Koesterich, who has become one of the company's most public spokesmen on investment strategy, will become head of asset allocation for the team, according to the internal memo provided by the company to Reuters on Thursday.

The mutual fund, which is BlackRock's largest, is keeping the same listed portfolio managers, including investor Dennis Stattman. The fund is a "multi-asset" portfolio of stocks, bonds and other investments.

Richard Turnill, who took on the global chief investment strategist title for the BlackRock Investment Institute during a broader reorganization earlier this year, and his colleagues are "taking on much of the firm's media and client-facing investment strategy responsibilities," the memo said.

The document was signed by Rich Kushel, who became BlackRock's multi-asset strategies chief during that reorganization, which was announced in January.

At that time, BlackRock Chief Executive Officer Larry Fink and the company's president, Rob Kapito, told staff in a memo that the Institute's mission was "expanding to include deeper research capabilities and an enhanced Investment Strategy function to deliver market insights even more effectively to clients."

Koesterich was a founding member of the Institute, an internal think tank that broadcasts the company's views on markets.

Koesterich, working from BlackRock's San Francisco office, had run the BlackRock's Model Portfolio Solutions (MPS) team, which does research on and manages some of the company's investment products. He featured regularly on business television as well as in news articles and wrote widely read commentaries on global markets.

He also was one of two portfolio managers on the company's four Target Allocation funds , which have $883 million in assets.

Vishal Karir is replacing Koesterich on those portfolio management assignments, while Kevin Holt, a 13-year BlackRock veteran, is taking over as head of the MPS team.

New York-based BlackRock, the world's largest asset manager, oversaw $4.6 trillion in assets globally as of Dec. 31, 2015.

(Reporting by Trevor Hunnicutt; Editing by Dan Grebler, Bernard Orr)

By Trevor Hunnicutt