For more than three decades Sir Martin Sorrell dedicated his life to transforming a small Kent-based manufacturer of shopping baskets, Wire and Plastic Products, into the world’s biggest marketing services group.

The question now for his successor, WPP’s investors and its tens of thousands of clients is whether the £15bn group can survive the departure of its founder and the dramatic changes the internet is bringing to the traditional world of advertising.

Sorrell’s unique relationship with WPP allowed him to run it autocratically with an iron hand – leading to a “Sorrellcentricity” that critics say had made it his personal fiefdom. These are methods his successor cannot hope to be allowed to employ.

Whoever takes over could find keeping such a sprawling empire together an almost an impossible task: WPP employs more than 200,000 staff in 400 separate ad businesses in more than 3,000 offices in 112 countries.

The era of advertising Sorrell ushered in has been about scale as a handful of big players – WPP, France’s Publicis and Havas, Japan’s Dentsu and New York-based Interpublic and Omnicom – have hoovered up smaller agencies. Sorrell, a former investment banker who cut his teeth in advertising as the Saatchi brothers first finance chief, was a master deal maker at the fore of the global land grab.

“Martin changed an industry inventing a lot of what became the model for the big holding company along the way,” says David Jones, the former global chief executive of Havas. “He was renowned for his financial acumen, but his PR skills were probably even stronger. He wasn’t widely liked but he was universally admired.”

But his departure, analysts say, raises doubts over WPP’s ability to withstand the core challenge facing the advertising behemoths: the internet. The rise of social media and Google and Facebook’s (hitherto unquestioned) advertising power has raised valid questions among advertisers. Big spenders like Marmite producer Unilever, Gillette maker Procter & Gamble and car giants like Ford are increasingly questioning who they spend their money with and whether big groups like WPP still offer the best model to create and buy their campaigns for them. If big is not necessarily better, is this not only the end of Sorrell but of the lumbering advertising group?

“Sorrell was relentlessly driven and competitive even at an age when most people had long since hung up their boots,” says Jones. “In the end technology caught up with him. It’s the end of an era but also maybe the beginning of the end for an industry.”