When Facebook paid $1bn for Instagram, people thought Mark Zuckerberg was off his rocker.

It was spring 2012, and the social network was just weeks away from going public. Would-be investors were already jittery that Facebook would struggle to make money long term, and here was its founder, writing 10-figure cheques for a rival that had never turned a profit.

He negotiated the deal personally, in a matter of days, only informing the board when it was pretty much done and dusted.

Facebook’s directors may have been irked, but Zuckerberg’s swoop turned out to be one of the best moves the company has made.

Instagram was very small at the time – it had just 11 staff – but the photo-sharing service had hit upon a successful formula. It was growing rapidly, and Zuckerberg knew it would become a potential threat to Facebook if he didn’t swallow it up first.