This spat is clearly personal, boiling down to the fact that Icahn simply does not like Ackman, alleging that he reneged on a deal in the past. Since then, Icahn, 76, has clearly held a grudge against the 46-year-old hedge fund manager.

The battle on CNBC in January between Icahn and Ackman was one of the most entertaining segments on financial television in years -- maybe ever. Icahn cursed repeatedly, saying he was given permission to say "whatever the hell I wanna say." He even accused CNBC host Scott Wapner of trying to bully him.

The amazing thing about this story is that it doesn't stop at Icahn and Ackman. Dan Loeb, another hedge fund heavyweight, recently announced that he owns 9 million shares, or 8% of Herbalife.

In a letter to investors, Third Point's Loeb refuted Ackman's claims that Herbalife is a pyramid scheme. "The pyramid scheme is a serious accusation that we have studied closely with our advisors. We do not believe it has merit," Loeb wrote in the letter.

Other hedge fund managers besides Icahn and Loeb have come out against Ackman. Robert Chapman of Chapman Capital and John Hempton of Bronte Capital have previously said Herbalife's business model is legitimate.

I've long suspected that many on Wall Street simply do not like Ackman, for whatever reason. Maybe it's the way he conducts himself in public, maybe it's the fact that he's achieved so much success (although Icahn could buy and sell Ackman a few times over). I don't know what it is, but there just seems to be something that people don't like about him.

Ackman responded to Icahn's investment, saying he welcomed it. Icahn appeared today on CNBC's Fast Money to talk about the investment. He said the investment is not personal, but rather that he's trying to make money, and that he believes Herbalife and MLMs are a great way to retail products.

Icahn took the time to throw a few jabs at Ackman, saying his 300-page paper "is nothing" and that there is no expert opinion in the paper. "If Ackman gets squeezed, I'm not going to feel sorry," Icahn said during the interview. "The fact that I don't like Ackman, you could say, is the strawberry on top of the ice cream."

No matter what happens in this battle of hedge fund heavyweights, one thing is clear. Whoever loses, whether it's Ackman or Icahn, the rest of us can expect more good times.

-- Written by Chris Ciaccia in New York

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