Billionaire activist investor Carl Icahn gave up his seat on the Yahoo Inc board of directors on Friday, closing a tumultuous chapter in the Internet company's 15-year history.

Icahn said in a letter to the board he did not believe Yahoo needed an activist investor as a director at this time, and that his attention was focused on other matters. The letter said his resignation was effective immediately.

Icahn won his seat on the board in July 2008, in the wake of Yahoo's protracted -- and ultimately fruitless -- talks with Microsoft Corp , which had offered $47.5 billion to buy Yahoo.

Yahoo CEO Carol Bartz in January replaced Jerry Yang, who had rebuffed the software giant's offer. Instead, Yahoo and Microsoft announced a 10-year search partnership in July, in which Yahoo will use Microsoft's back-end search technology on its Web portal.

In his letter, Icahn said he believed the Microsoft transaction would provide great long-term benefits to Yahoo and commended Bartz on a great job.

A Yahoo spokeswoman said on Friday there were no immediate plans to find a replacement for Icahn, and that the board would operate with 11 directors for the time being.

Carl has been an important member of our board and has helped us through some significant transitions, Yahoo Chairman Roy Bostock said in a statement. We are all grateful for his active role shaping the future of Yahoo.

Shares of Yahoo were off 25 cents at $16.97 in after hours trade.

Icahn is chairman of Icahn Associates and currently sits on the boards of several companies including Blockbuster Inc and American Railcar Industries Inc .

ICAHN PROUD

He owned 62.8 million shares for a roughly 4.5 percent stake in Yahoo as of August 31, according to Reuters data. Icahn amassed the bulk of his Yahoo stake in May 2008, according to media reports at the time, when shares of the company were trading in the low- to mid-$20 range.

After Yahoo rejected Microsoft's offer that spring, Icahn mounted a proxy contest to try and oust the Yahoo directors, eventually reaching a settlement that gave Icahn and two of his handpicked director nominees seats on the company's board.

When I joined the board, the company was in a state of turmoil. In the period since then, we have all worked together to achieve much for the company, most notably bringing Carol on to be the CEO and then consummating the search deal with Microsoft, Icahn said in his letter.

I am proud to have played a role in both these decisions.

Yahoo has said the search deal with Microsoft, which is awaiting regulatory approval, will allow it to save $425 million in operating expenses and enable them to mount a more effective challenge to search leader Google Inc .

Last week, Yahoo reported its third-quarter net income tripled thanks to cost-cutting and asset sales.

Icahn sold nearly 13 million Yahoo shares between August 27 and August 31 at prices ranging from $14.75 to $14.92, according to an SEC filing.

(Editing by Edwin Chan; editing by Carol Bishopric)

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