Martin Sorrell has made a shock departure from WPP amidst allegations of personal misconduct.
Sir Martin denied any wrongdoing after the allegations surfaced earlier this month, but said he understood the company had to investigate it.
He added in a letter sent to WPP staff: "As I look ahead, I see that the current disruption is simply putting too much unnecessary pressure on the business, our 200,000 people and their 500,000 or so dependents, and clients we serve in 112 countries".
The company said Sir Martin will be treated as having retired, with chairman Roberto Quarta becoming executive chairman until a new chief executive has been appointed.
WPP, which will consider internal and external candidates to succeed Sir Martin, faces complex set of challenges.
Sorrell, who has denied any wrongdoing, took over WPP as CEO in 1986, and through an audacious series of acquisitions transformed the United Kingdom maker of wire shopping carts and animal cages into a modern advertising holding company that today has over 200,000 employees across its businesses. "However, I believe it is in the best interests of the business if I step down now".
The advertising titan resigned Saturday night as WPP announced that an investigation into the matter had concluded, with the firm saying only that "the allegation did not involve amounts that are material". He is one of the most high profile, and best paid, executives in the country.
The acquisitions included the J. Walter Thompson Group, the Young & Rubicam Group and the Ogilvy Group.
He previously worked at Saatchi and Saatchi, and was knighted in the Queen's New Year honours list in 2000. Some of its biggest clients say it has an unwieldy structure and point out that professional services firms such as Deloitte and Accenture are encroaching on traditional advertising turf. "The founder CEO has over 30 years' service with the company and is identified with the success of the group's strategy and a failure to plan for his succession could impact investor confidence in the company", it acknowledged.
The company said Sorrell would be available to assist with the transition, and the man synonymous with the British marketing group told the staff they would come through this hard time.
WPP spends on those platforms on behalf of clients, taking a cut-Sorrell has said WPP spent about $5 billion with Google and $2 billion with Facebook previous year. "Good fortune and Godspeed to all of you".