I looked at the queue waiting for the session that rivalled my own panel at the end of the first day at Advertising Week Europe on Monday and nodded in appreciation of who it was for. Every year Sir Martin Sorrell is one of the week's biggest draws and it was no exception this year.
It's the same each year at Ad Week New York and will be the same next month at the first Ad Week Asia too when it takes place.
Without debate, Sir Martin (and his £63m bonus) is box office. He is probably the only person in the industry who has the mainstream media the world-over eating out of the palm of his hand.
And there in is part of the problem for the succession of the next chief executive of WPP.
Don't get me wrong - I don't think he's ready to hang up his hat quite yet - although it is coming - and the next leader of the world's largest network of advertising agencies has a hell of a job on his/her hands. It's like succeeding Sir Alex Ferguson - an unenviable task.
Not only does that person need to be a very shrewd businessperson but they also need to have gravitas and the ability to marshal a group of shareholders who are not shy in offering their collective point of view.
Also - that person will need to consider how does WPP continue its growth strategy? They are very likely to continue a similarly active acquisition policy - and so they will live in Sorrell's shadow until they can find their own way forward. It is important that WPP remains number one in terms of size, of that there is no question.
Perhaps becoming the manager of Manchester United is easier in reality.
Sorrell definitely believes that the next boss at WPP needs to be steeped in digital and have experience of successfully guiding a global marketing business. Knowledge and experience in developing markets will also be preferred. It's no secret that is where Sorrell sees the future of sector growth, a vision shareholders will doubtless continue to agree with.
As with my suspicions on Levy's successor at Publicis Groupe, my belief is that person will come from within. However not many people will have a clear favourite candidate at this time on who it might be. Again, the shareholders will need to approve the choice when it is announced too.
We're probably looking at someone with the experience of the bosses at GroupM - chairman Irwin Gotlieb, its president Dom Proctor, US chief exec Brian Lesser or digital head Andrew Scott. There's also a strong shout for Mark Read at Wunderman, Eric Salama, Kantar's CEO or possibly Lindsay Pattison from Maxus could be a shrewd move too.
If I were asked to bet on who it will be I'd be tempted, but Sir Martin has always been good at throwing a curve ball.
It's difficult to imagine what WPP will become without the current boss at the helm, but the day is fast approaching. Even so, Sir Martin will still make an appearance or two at Advertising Week and pull in the punters, even in retirement (a notion he probably doesn't dwell on too often.)
There's still life in the old dog yet though. I promise you that.