Those ludicrous ideas that made a billion

As with many great inventions, the premise sounds faintly ridiculous: an undergarment that gives women of any shape a Hollywood-style figure.

But the inventor of Spanx, Sara Blakely, is now, at the age of 41, the youngest woman to make Forbes Magazine's billionaire list after her company was valued at $1bn (£633m) last week. But she's not the only billionaire inventor to have had the foresight and faith to see her idea through from conception to product after others scoffed.

Here's six of the best:

Michele Ferrero

Ferrero Rocher; £12bn

The must-have dinner party treats were derived from a simple hazelnut and chocolate spread, created by Michele Ferrero in 1963.

Mark Zuckerberg

Facebook; £11bn

Facebook connected 500 million people across the world and inspired a Hollywood film along the way – as well as generating its founder £11bn – not bad for a college drop-out. At 27, Mark Zuckerberg is the second-youngest billionaire in the world.

Howard Schultz

Starbucks; £1.5bn

From humble beginnings selling pots and pans, Brooklyn-born Howard Schultz's notion that coffee should be an experience rather than just a drink revolutionised consumption of the drink across the world.

Daniel Abraham

Slim-fast!; £1bn

As the inventor of this easy form of dieting, the US army veteran from Long Island sold the idea of "a shake for breakfast, a shake for lunch, and a sensible dinner" to the world.

Birgit Rausing and family

Tetra Pak; £10bn

Birgit Rausing is now Sweden's third-richest person, thanks to her father Ruben's invention of waterproof paper in 1951 and the storage cartons for liquids, an idea he had in the 1940s.

Pierre Omidyar

eBay; £4bn

Originally given the seriously un-catchy name AuctionWeb, the internet marketing site was devised by Paris-born Iranian-American, Pierre Omidyar, 44, and is now a huge global enterprise.