In August 2007, billionaire Carl Icahn took hold of 2.7 million of Biogen Idec’s shares, making him one of the company’s largest investors. Over the next few years, he grew his ownership in the Weston, Massachusetts-based biotech, holding 8.2 million shares valued at nearly $750 million as recently as June of this year. But yesterday, after four years of attempted control of the company’s direction and management, Icahn disclosed that he has dumped all of his stock in the company, according to the Wall Street Journal.

Ever since he first invested in Biogen Idec, Icahn has tried to wrench control of the drugmaker best known for its drugs for treating multiple sclerosis. He insisted that the board sell Biogen Idec at the end of 2007, and when they failed to find a buyer, Icahn accused them of lying about their effort. In 2009, the board elected two of his four nominated directors at his urging — and two months later, two other board members resigned (although former director Cecil Pickett told Nature that early resignation was “the plan all along”).

His sudden sale of all Biogen Idec stocks suggests that Icahn is fed up, despite his hard work to steer the company’s board and research. Instead, he has taken interest in Forest Laboratories — and it feels like déjà vu. Icahn says he wants to trim the New York-based biotech’s R&D efforts, in a similar move to one he pulled at Biogen Idec. And he’s even nominated four of his own associates to the board, an effort that the company is actively resisting.

“We believe Icahn has offered no good reasons to elect his hand-picked nominees, who lack operational experience, have in our view significant conflicts of interest and have shown themselves as not understanding Forest’s business,” Forest’s current board wrote in an open letter to its shareholders.

Icahn also sold his shares in the biotech companies Amgen, headquartered in California, New York-based Regeneron, and medical device company Cyberonics from Houston, Texas.

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