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It is given to very few - I can think of Sir Alex Ferguson - to decide the time of their own departure.

Although Sir Martin Sorrell is deemed to have "retired" from WPP - as far as the rules regarding his ongoing share grants are concerned - this was not the outcome he wanted, at least not now.

His legacy as one of the titans of the advertising industry is secure.

Sir Martin built a £20bn global business from scratch, amassing a personal fortune, and his views on trends in world business were much sought after around the globe.

In the end, it was the trends in world business that wrong-footed the sprawling empire he created.

The old advertising and media-buying WPP agencies have been rendered less important by the sheer reach and analytics available by going to the mega-platforms Google and Facebook direct.

By his own admission, WPP got "walloped" last year and the company has lost a third of its value. If it hadn't, it's possible Sir Martin could have survived the recent investigation into his conduct involving amounts of company money the board deemed immaterial.

But shareholders were getting restless. He had lost the unanimous backing of the board and, at 73, he is no spring chicken by chief executive standards.

Sir Martin is a man of enormous energy and you wouldn't put it past him to create a new media empire. But his life's work, WPP - a company he was often accused of treating as his own - will now be run by someone else.

It could be a difficult succession. Whatever Sir Martin says about a smooth transition, the fact that the chairman, Roberto Quarta, is stepping in to run the company shows the ground had not been properly prepared.

I've never met anyone who could explain any logic behind the way WPP's empire was constructed, and shareholders are now ready for a change.

That could mean the break up of a company that had become in the words of one shareholder "too big, too unwieldy. He tried to meet new challenges in the market by just adding more companies. It needs to shrink to grow".

Only one man seemed to really understand how the empire was built and that was Sir Martin Sorrell. For 30 years that was good enough.