Billionaire activist investor Carl Icahn on May 19. (Victor J. Blue/Bloomberg News)

One of the world’s richest men. A ruthless corporate raider. A brilliant loner. A philosopher and chess player, always thinking 10 moves ahead of you. The phone call that CEOs can't afford to ignore. A Rhodesian Ridgeback going for the jugular of corporate lions.

These are some descriptions of Carl Icahn, the 79-year-old investor whom Forbes ranked as the world's 31st richest person in 2015. Icahn's name has been in the news for decades, mostly because of his battles with the executives of dozens of high-profile companies.

Now Icahn is once again in the spotlight, as his longtime business contact, friend and rival Donald Trump, the front-running Republican candidate, says he will nominate Icahn for treasury secretary.

Icahn is a fascinating figure, seen as a kind of financial Robin Hood by some and a misanthropic attack dog by others – often depending on whether the speaker has been in Icahn's scope. Icahn grew up in the lower-middle-class neighborhood of Far Rockaway, Queens, and still retains a Queens accent, relatively modest tastes for one of the world's richest men, a working class identity -- and, some would say, a chip on his shoulder.

Icahn, who has not responded to requests for comment, made his name as a corporate "raider" in the 1980s. He was among a group of activist investors who engaged in a practice called "greenmailing" -- a portmanteau of "greenback" and "blackmailing," in which investors would buy up a company's stock and threaten a hostile takeover. The company would be forced to buy its stock back at a premium to stop the takeover, enriching the investors.

A 2001 handout photo of billionaire financier Carl Icahn. AP Photo A 2001 photo of billionaire financier Carl Icahn. (AP)

Supporters have long seen Icahn as a force for market efficiency, willing to shake up complacent CEOs and demand that companies invest their cash in more profitable ways. But others paint him as a predator who strips companies of their most profitable assets and employees of their jobs.

The reputation is due in part to his notoriety as the leader of now-defunct airline TWA. In 1985, he carried out a hostile takeover of TWA and pledged to make the troubled airline profitable. But over the next few years, he sold off some of the airline's prize assets and took it private, a decision that allowed Icahn to regain his investment but left the company saddled with debt. By 1992, TWA filed for bankruptcy.

Mark Stevens, the CEO of marketing strategy firm MSCO.com and the author of a biography called "King Icahn," who lived near Icahn and played tennis and vacationed with him, recounts a meeting between TWA executives and Icahn. Icahn had an egg in his pocket, and he took it out and held it extended in his hand, Stevens said. "He points to his hand, and he says, 'This is me.' And then he points to the egg and says, 'This is you. So you decide in our negotiation right now whether I squeeze you,'" Stevens recalled.

In 1991, Congress passed legislation to try to keep Icahn from leaving the government on the hook for up to $900 million in TWA employee pensions. The bill allowed the government to seek unfunded pension liabilities from Icahn's other holdings, potentially bankrupting him. Stevens said he urged Icahn to set some money aside in a separate bank account to protect himself, but Icahn refused to do so. "My money is my army. I need my army around me," Icahn said, according to Stevens.

Through the decades, Icahn was a prominent investor in dozens of listed companies, including Texaco, RJR Nabisco, Viacom, Motorola, casino operator Tropicana Entertainment, Netflix and car-sharing service Lyft. He bought out struggling casinos in Atlantic City and went head to head with the unions who protested benefit cuts and layoffs. More recently, Icahn's wealth has blossomed with the dramatic rise in value in his shares of Apple, as well as investments in energy and railway companies that benefited from America's shale gas boom.

Since the financial crisis, Icahn shifted away from managing other people's money, instead mostly going it alone. His hedge fund lost substantial amounts of money during the financial crisis, like almost all funds did, and in 2011, Icahn decided to give back the rest of the outside capital in his fund. Now, he owns more than 90 percent of Icahn Enterprises, a public company with majority stakes in more than half a dozen companies.

Secretary Icahn

Icahn seemed surprised and initially balked when Trump mentioned his name as one of three potential treasury secretary nominees in a televised interview in June. In a statement on his Web site, Icahn responded that he was "flattered but do not get up early enough in the morning to accept this opportunity."

But Icahn apparently came around. In August, Icahn said in a series of tweets that he would accept the secretary post if offered it. He called America's methods of electing corporate and political leaders "completely dysfunctional" and said "in both areas, we are in dire need of a breath of fresh air."

Early Tuesday morning, Icahn released a video on his site explaining his reasons for supporting Trump, as well as some broader concerns about the financial markets and the economy.

In the video, called "'Danger Ahead: A Message from Carl Icahn," Icahn praises Trump for being "not beholden to an establishment." "Maybe he's brash, but he's willing to say what he believes, and he's willing to say this is complete bull----," Icahn says in the video.

In the video, Icahn offers his support for a few of Trump's tax ideas and explains why. He backs Trump's plan to end the carried interest tax loophole, which reduces taxes for hedge fund and pension fund managers.

Icahn also argues for lowering the tax that companies must pay on repatriated earnings from abroad, saying U.S. companies have earned $2.2 trillion in profits abroad but won't bring the money back to the U.S. because America imposes a double tax on their earnings.

Icahn also criticizes the Federal Reserve for keeping interest rates so low for so long -- an environment that he says is creating a dangerous asset bubble -- as well as corporate leaders for their short-term thinking.

Although interest rates are at all-time lows, companies aren't investing in real and profitable assets, instead choosing to put their money into acquiring other companies and buying back their stock, short-term moves that make them appear more attractive to investors. "The earnings that are being put out today, I think they’re very suspect," Icahn says.

"I’ve been around a long time," he says at the end of the video. "I saw it in ’69, ’74, ’79, I tell you, ’87, and 2000 wasn’t pretty. And I think a time is coming that might make some of those times look pretty good. . . . The public, they got screwed in ’08. They’re going to get screwed again,” he says.

Icahn, like Trump, is clearly painting himself as a defender of the little guy. Stevens, the biographer, argues against this interpretation. He describes Icahn as an honest and honorable person, and a brilliant negotiator, but one with little respect for the idea of fairness, who once called the idea of a fair deal "a trap." His philosophy is "very Nietzsche," Stevens says.

It's a long road for Trump to the executive office, and an even longer one for Icahn to a Cabinet position. But if they get there, Stevens cautions that a strong personality like Icahn could easily clash with President Trump. "Carl is a funny guy and he loves to do impersonations of people. The one person he made fun of more over the years was Trump," he says.

There's another reason for potential conflict between the two. Both Trump and Icahn clearly believe money talks. By that measure, Icahn has by far the louder megaphone. According to Forbes, Icahn has a net worth of $23.5 billion compared with Trump's $4.5 billion.

This post has been updated.

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