Where there is trouble, chances are good billionaire Carl Icahn won't be far from view. The corporate raider has a penchant for taking over companies, replacing bungling executives, and boosting value. His arrival yesterday at the doorstep of troubled generic-drug maker Mylan Laboratories (NYSE:MYL) could be bad news for Mylan's management but good news for shareholders.

Mylan has been stumbling lately. Things went from bad to worse in July with Mylan's decision to acquire King Pharmaceuticals (NYSE:KG). The deal is a stinker. Mylan is paying $4 billion for a poorly performing company that's under investigation for its trading and financial reporting practices. Even worse, King may not deliver a big punch in the branded cardiac drug business that Mylan hopes to enter. On announcing the deal, Mylan stock went into a tailspin and has been hovering near its 52-week low.

Yesterday, Icahn got the green light from regulators to purchase up to 11.9% of Mylan shares. His move need not be the first stage of a hostile takeover, since he has not officially stated his motives. Mylan stock shot up 10% yesterday, so he could conceivably walk away with a tidy profit.

Negotiations are more likely. Expect talks when Icahn eventually meets up with Mylan's top brass, not a punch-up. Mylan CEO Robert Coury will try to calm down shareholders and prevent them from joining forces with Icahn to win a proxy fight.

Even so, Mylan executives should be scared. They openly remain committed to an acquisition that, judging by the share price, a lot of shareholders don't like. This could be the dawn of a management shake-up.

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Fool contributor Ben McClure hails from the Great White North. He doesn't own shares of either company mentioned here.