Carl Icahn is up to his usual tricks.

The “activist investor” has been involved in an attempt to gain control of the board of directors at Biogen Idec (Nasdaq: BIIB), a leading biotechnology company. His end game is to force a sale of the company. If he is successful, it could mean big gains for shareholders.

And more than a few bucks for himself. Icahn is one of those guys Wall Street loves to hate.

In July, Biogen CEO Phillip Sharp said he would retire from the board even though his seat wasn’t up for reelection until 2011. Sharp, a Nobel laureate who co-founded the company, had served on the board since 1982.

Icahn nominated three candidates for four open seats in 2008 but failed to win a single one. In February 2009, Icahn nominated four new candidates at the next round of elections. This time he won two seats. Sharp’s retirement created another vacant spot. It also removed a strong voice of opposition to Icahn’s plans.

Then came news that Cecil Pickett, head of Biogen’s research and development division, would retire and leave the board Oct. 5. The company had said in March that Pickett would step down as head of R&D.

Pickett fell into Icahn’s crosshairs in May, saying the company had “failed leadership,” citing specifically a “lack of R&D focus.”

With Pickett gone, Icahn now has an even better chance to make changes at the company. Another vacant board seat filled by an ally is an obvious advantage, but the R&D vacancy also presents an opportunity.

One of Icahn’s main arguments during his first attempt to seat his own board members was that Biogen hadn’t brought a new drug to market in five years. If the company can show it is serious about developing new drugs, now would be the chance to prove it. Sales of Tysabri, one of Biogen’s top-selling multiple sclerosis drugs, are growing, but concerns about side effects could hurt sales.

Last week, Biogen launched a bid to buy Facet Biotech (Nasdaq: FACT). The two companies are working on a multiple sclerosis treatment that hasn’t yet reached the market. If Biogen can earn more from its drug pipeline after the Facet merger and renew its focus on R&D, the company would increase its appeal as a takeover target.

Icahn will continue to push his R&D agenda — there’s little doubt about that. And there’s even less doubt he will try to use the vacant board positions to seat his own members. If either happens, the takeover case for Biogen looks even better.

This is how Icahn operates. If he isn’t able to convince the company to bend to his will outright, he engages in a war of attrition. And Icahn appears to be winning this one.

The bright side for investors is that Carl Icahn’s track record speaks for itself. With an estimated net worth of $14 billion, Icahn uses all of the means at his disposal to unlock value for shareholders. When Icahn is involved, it’s not uncommon for a company to be sold, broken up into smaller pieces or to announce a share buyback.

If Icahn garners enough support, the big drug companies could come knocking with a lucrative offer in the not-too-distant future. For investors willing to bet on another Icahn deal, these shares are very tempting.