Tweet heard ’round the stock market makes Carl Icahn Apple’s unlikely white knight

In the past months, Apple chief Tim Cook has had to deal with an increasingly indifferent press and an outright hostile stock market that pummels the company’s every move, despite its stellar success.

Enter this story’s unlikely white knight: billionaire investor Carl Icahn, who, with just  one tweet (picture above), has single-handedly managed to raise the company’s stock by nearly five percent in less than twenty-four hours. This may not sound like much, but, given Apple’s size, that means that investors in the company are now roughly $15 billion dollars richer. It seems when Icahn expresses confidence in both Apple and its chief executive, the market finally listens.

History of a corporate activist

What makes Icahn’s remarks so significant is that the 77-year-old billionaire is not exactly known for his cozy relationships with corporate executives. Born in Queens, New York, in 1933, he began his career as a stockbroker on Wall Street, and moved on to buying significant portions of public companies in 1968, becoming very rich in the process.

Since then, he has been involved in some of the most contentious hostile takeovers of the last four decades. In 1985, he took control of the once-mighty airline TWA, and sold off many of its assets to pay off the debt incurred during his leveraged buyout; by the time he sold it off in 1993, he had made a cool $469 million in the transaction—not to mention giving a travel company he owned a ticket-booking deal so sweet that the only way the airline managed to get out of it was to enter bankruptcy proceedings in 1995.

In the intervening twenty years, Icahn has become famous for picking fights with a who’s who of corporate giants in which he invested, including U.S. Steel, Time Warner, Blockbuster, and Yahoo, where he famously advocated for the dismissal of co-founder Jerry Yang in order to pave the way for a Microsoft acquisition. Nor does it seem that the years have softened him any: on Wednesday, his company is due in court to litigate a lawsuit it launched earlier this month to prevent entrepreneur Michael Dell from taking the computer manufacturer that bears his name private.

Strange bedfellows

Given his outspoken activism, it should be obvious that Icahn is not someone you often see enthusiastically endorsing a company or its chief executive. And yet, here he is, announcing that he has taken a large interest in Apple—estimates have put it north of $1 billion—and that he seems to be happy with the company’s overall direction and future prospects.

Icahn’s words come as good news for Apple, given the choir of increasing disappointment that has surrounded Cupertino’s every move in the last eighteen months, such as the bleak remarks made by Oracle CEO (and close Steve Jobs friend) Larry Ellison in an interview with CBS’s Charlie Rose and, earlier this year, in a panel discussing the late Apple-co founder’s legacy at the D10 conference.

Still, I can only imagine that the activist billionaire’s interest in any corporation would send shivers down its CEO’s spine. For its part, though, Apple doesn’t seem to be worried: In a statement to various news oulets, Apple’s PR department said that it “appreciates the interest and investment of [its] shareholders,” and that Cook and Icahn had a “very positive” phone conversation.

It may seem like a remake of The Odd Couple, but maybe, just maybe Icahn’s playing against type here, bolstering the world’s most prominent tech company instead of just tearing it down.