Now there are 60-odd million in the world, nearly one for every 100 people - not bad for a humble bookcase.

In fact, so ubiquitous are they, Bloomberg uses them to compare purchasing power across the world.

According to the Bloomberg Billy Bookcase Index - yes, that's a thing - they cost most in Egypt, just over $100 (£79), whereas in Slovenia you can get them for less than $40 (£31).

A few of the interesting stats on Ikea's Billy bookcase series.

To get as rich as Mr Kamprad has, you have to make stuff that is both cheap and acceptably good.

And to get even richer, you make stuff that is both cheap and the best in its class, though that's not as easy with furniture as it is with software.

IKEA is an interesting example of disruption that I haven't read as many think pieces on as the usual suspects in tech.