He took a United Kingdom manufacturer of wire baskets and built it into a worldwide provider of advertising, public relations and marketing services through a series of takeovers.
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.
And last month amidst slowing down of revenues and income and the growing clout of the FANGS - the board commenced an investigation charging Sorrell with personal misconduct and misuse of the company's assets. These are methods his successor can not hope to be allowed to employ.
Beyond its advertising strength, WPP has been a presence in Hollywood as well - with the firm investing in The Weinstein Company in 2005. One New York-based executive told Reuters how, on a night out, senior executives would all email Sorrell at exactly the same time to see who he would respond to first.
Roberto Quarta, WPP's chairman, will become executive chairman while a permanent successor to Sir Martin is identified, according to insiders. "He was renowned for his financial acumen, but his PR skills were probably even stronger".
In a statement to WPP employees, Sorrell said the current disruption was putting "too much unnecessary pressure on the business" and that in the interest of the company and clients it was "best for me to step aside".
WPP said that the probe had concluded, adding "the allegation did not involve amounts that are material".
WPP CEO Sir Martin Sorrell has stepped down from the holding group that he led for the past 33 years, following an an internal investigation into one of the marketing industry's most powerful executives. "Good fortune and Godspeed to all of you ... now Back to the Future". (He is renowned for holding conversations while texting with clients and friends.) Today, WPP can be a global advertisements behemoth with 130,000 workers in 112 countries, and a industry valuation of approximately 2-2 billion pounds, or about £ 31 billion. WPP's financial guidance has repeatedly proved too optimistic, and its shares have lost a third of their value over the past year - far more than rivals facing the same market challenges of reduced ad spending and competition from web giants. His share awards will be pro-rated in line with the plan rules and will vest over the next five years, to the extent Group performance targets are achieved.
Chairman Roberto Quarta takes over as executive chairman.