There's life in the old billionaire yet. The world's third-richest man, Warren Buffett, has shown the world a whole new side of himself by donning a purple bandana, an Axl Rose wig and fake tattoos to belt out a rock ballad for staff at his US insurance company, Geico.

In a promotional video rapidly going viral on the internet, the 79-year-old tycoon, nicknamed the "sage of Omaha" for his legendary stockpicking prowess, joins employees in a somewhat cheesy number called "All for you"‚ which trumpets the importance of customer service.

Buffett's husky midwestern tones cut in at about the two-minute mark and perhaps we should charitably advise him not to give up the day job. A commentator at Toronto's Globe and Mail compared his singing prowess to "a drunken Neil Young".

Irrespective of his musical merits, you've got to admire the leather-clad Buffett for being game. It's hard to imagine his younger rivals on the global rich list, Carlos Slim or Bill Gates, rocking out in quite the same way.

Geico, which has been fully owned by Buffett's Berkshire Hathaway investment empire since 1996, has been a major moneyspinner for Buffett, who built his early fortune on insurance. In his annual letter to shareholders this year, Buffett boasted that the business had made an underwriting profit for 13 of the 14 years under his ownership.

"I became excited about Geico in January 1951, when I first visited the company as a 20-year-old," wrote Buffett. "I'm even more excited today."