Simple ideas that made a fortune

How often have you seen a popular new product or service and thought: that's just so simple? Genius doesn't have to be complicated; after all legend has it that Issac Newton invented the cat flap.

But just because it's not complicated doesn't mean it can't make the inventor money. Take Sluggie's slanket, effectively a backwards dressing gown. In the first year of marketing the company reportedly sold more than four million units. We imagine their pockets felt pretty snug after that too.

So we decided to take a look at some of the simple ideas that made their inventors rich beyond all expectations...

Have you ever thought of marketing a brilliant idea? Have you used any of these products? Do their inventors deserve their wealth? Have your say using the comments below.

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Could your invention make you millions?