Biogen Idec's executive chairman to retire this month

William H. Rastetter, the executive chairman of Biogen Idec Inc. who built Idec Pharmaceuticals of San Diego into a major biotechnology firm and helped orchestrate its merger with Biogen Inc. of Cambridge, will retire at year's end, the company said.

Bruce Ross, a Biogen Idec director who served on Idec's board before the 2003 merger, will become nonexecutive chairman Jan. 1. James C. Mullen will continue as president and chief executive.

Rastetter is an imposing presence who is well-known in such diverse fields as biochemistry, photography, and healthcare policy. He kept a low profile since Biogen and Idec merged in November 2003. Biogen Idec purchased a $1.7 million condominium in a luxury tower in Cambridge for Rastetter to live in when he was in the area, but he avoided publicity and was rarely seen at local biotechnology events.

''I am proud of all that we have accomplished in implementing the integration of Biogen and Idec and establishing a platform for future success," Rastetter said in a statement. He declined to be interviewed.

Rastetter's departure didn't rattle Wall Street or investors.

''We've been anticipating Bill's eventual bowing out gracefully from the scene, as he's been in the game for a long time and maybe it was time for him to move onto other things," said Jennifer Chao, an analyst with Deutsche Bank.

''We told clients we weren't surprised by the announcement," said Ronald Renaud Jr., an analyst at JPMorgan Chase. ''You had two CEOs that stayed on board after the merger, and eventually that's got to fizzle out."

Biogen Idec this year said it was selling several key assets that it acquired with Idec, including a new manufacturing plant in Oceanside, Calif., and other West Coast facilities. Renaud predicted Biogen Idec's presence in California will continue to shrink.

''I'm not sure it could go away completely, but it will be minimized to the smallest presence possible," he said. The company maintains a cancer research center in San Diego.

At Idec, Rastetter championed the monoclonal antibody that became Rituxan, one of the most successful cancer drugs ever. He also negotiated a commercialization agreement with Genentech Inc. that provided a windfall for Idec when the drug's sales far exceeded initial expectations.

In 2005, Biogen Idec's activities were dominated by Tysabri, the multiple sclerosis drug that was expected to be a blockbuster. The company voluntarily suspended sales after a patient in a clinical trial was diagnosed with a rare brain disease. The company launched an investigation of all patients who took the drug in trials, and began negotiations with regulators about bringing Tysabri back to the market. It also began a major restructuring focused on cutting costs and obtaining new drugs to sell through partnerships and licensing.

None of that would have appealed to Rastetter, said a longtime friend.

''Bill is a brilliant scientist and chemist," said Kurt Von Emster, a general partner at MPM Capital. But, Von Emster said, Rastetter is more interested in research and development ''and the company is now focused on cost efficiency."

In 2004, Rastetter earned a base salary of $940,256 and bonus of $1,345,200. According to details of an employment agreement included in merger disclosures, Rastetter would receive a lump-sum payment of three times his salary and three times his target bonus if his employment were terminated for any reason other than for cause. He is also slated to receive 150,000 shares of restricted stock, according to the company's most recent proxy statement.

A spokesman said details of Rastetter's severance were being negotiated. Plans for the 2,150-square-foot condo in East Cambridge have not been finalized.

Jeffrey Krasner can be reached at krasner@globe.com.