Yahoo!

(YHOO)

unveiled a new chief executive and chairman and announced that its former top dog would be taking an even more diminished role at the Internet company.

The company said Terry S. Semel, the former co-chairman of

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Time Warner's

movie and music division, will be Yahoo!'s new chairman and chief executive, effective May 1. Tim Koogle, who decided last month to step aside as CEO, is now also turning over the reins as chairman to Semel. Koogle will become vice chairman, which will be what the company called a "transitional role" that he is expected to hold until August. He will remain on the board of directors.

Yahoo! President and Chief Operating Office Jeff Mallett and Chief Financial Officer Susan Decker will retain their current roles and report to Semel, the company said.

The naming of Semel ends an extensive, high-profile search for a CEO of the company, which has struggled lately amid a brain drain among its executive ranks and as the withering advertising climate online has diminished revenue.

When posting quarterly results that beat twice-lowered forecasts last week, Yahoo! announced plans to lay off about 400 staffers.