(CBS News) Investors will be watching the weight loss product company Herbalife closely Monday.
Its stock price went on a roller-coaster ride after two billionaire investors argued about the company -- and each other -- on live television.
The names Bill Ackman or Carl Icahn may not ring a bell, but on Wall Street, they're legendary investor activists. On Friday, the two titans of finance revived a decade-old feud that went viral and raised big questions surrounding the weight loss supplement maker.
As the founder of Pershing Square Capital Management, Ackman controls about $12 billion in assets, and he has his sights set on Herbalife. Ackman said in one broadcast, "How is it possible that Herbalife sells six times more nutrition powder than Abbott Labs, Unilever, and GNC?"
The answer? Ackman says Herbalife is a pyramid scheme. He's so sure of it, he's shorting Herbalife stock and betting $1 billion it will plummet to zero.
When the hedge fund manager went on CNBC Friday, the share price dropped to its lowest point of the day. Ackman said, "We believe this is a company causing enormous harm to millions of people and has done so over a very long period of time."
But minutes later, the price soared when another activist investor, Carl Icahn -- who won't say whether he owns Herbalife stock -- called in and accused Ackman of trying to manipulate the markets.
Icahn said, "He got a bunch of innocent investors, retirees, they are going to lose their money so Ackman can show a good record at the end of the year."
At times, the insults turned very personal, as the two traded blows over Herbalife and a long-simmering feud -- a business deal that ended up in court, where Icahn lost.
Icahn said, "Ackman is a liar. ... The guy is a major loser."
Ackman said, "This is not an honest guy, and this is not a guy who keeps his word."
Brian S. Sozzi, NBG Productions chief equities analyst, said, "The issue seems to be dating back many many years, and maybe it was festering beneath the surface. There is serious bad blood."
Herbalife has called Ackman's allegations "a malicious attack on Herbalife's business model, based largely on outdated, distorted and inaccurate information."
But all that took a back seat as Wall Street was riveted by the theater of two powerful billionaires airing their grievances, laced with Icahn's expletives.
Sozzi said, "They are what I call 'market movers.' When these guys talk, as an analyst or an investor, you tend to listen."
CBS News' Rebecca Jarvis spoke with Ackman Sunday night. He called the exchange with Icahn on CNBC a sideshow. But said he doesn't regret it. He believes it brought attention to what he calls the fraud taking place at Herbalife. Herbalife has yet to respond to the exchange. We're certain to hear more from company executives by the Feb. 19 earnings call.
The Securities and Exchange Commission is now investigating Herbalife, but has not yet decided whether to take action.
Ackman has been and will continue to visit with federal and state regulators. He told CBS News he's compiling a list of questions for Herbalife. Herbalife says ask anything, and we'll answer it on the record. Ackman said he's planning to make those answers public.
For more on this story and to watch Jarvis' full report, watch the video in the player above.