So much sweat, toil and cash was spent on the development of the Mercedes-Benz S-Class W140 that it was nicknamed the Billion Dollar Car. At the time, it was the most refined and luxurious saloon you could buy, and as a result the German brand sold nearly half a million of them over its seven-year lifespan.

If you’re the sort of person who finds the S-Class interesting (and who could blame you?), you’ll probably understand why the luxury saloon acts as a pioneer of new technology - and never more so was this the case than with the W140.

But aside from the self-closing doors, double glazing and surprisingly rocky reception at the 1991 Geneva motor show, what else makes this car so interesting? Read on to find out…