Martin Sorrell is stepping down as chief executive of WPP, the world's largest advertising agency, following allegations of personal misconduct.

Sorrell, who built WPP into a global brand during his 33 years at the helm, had been accused of misusing company assets. He has denied any wrongdoing.

WPP stunned the market last week when it said it had appointed lawyers to investigate alleged misconduct by Sorrell, aged 73.

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."

"As I look ahead, I see that the current disruption is simply putting too much unnecessary pressure on the business," Sorrell said in a statement to WPP staff. "That is why I have decided that, in your interest, in the interest of our clients, in the interest of all shareowners both big and small, and in the interest of all our other stakeholders, it is best for me to step aside."

Chairman Roberto Quarta will lead the company until a new chief executive has been chosen.

Sorrell is a titan of British business who was named the world's second-best performing CEO in 2017 by the Harvard Business Review. He took a U.K. manufacturer of wire baskets and built it into a worldwide provider of advertising, public relations and marketing services through a series of takeovers.

The acquisitions included the J. Walter Thompson Group, the Young & Rubicam Group and the Ogilvy Group.

He was richly compensated for his efforts.

Sorrell was the highest-paid CEO among FTSE 100 companies in both 2015 and 2016, according to a study released last year by the Chartered Institute of Personnel and Development and the High Pay Centre. He received £70.4 million ($100.3 million) in salary, bonuses, incentive rewards, pension payments and other benefits in 2015, and 48.1 million pounds in 2016, the study found.

"If WPP does well, I do well," he told the Press Association in April 2016. "Most of my wealth, if not all of it, is and has been for the last 31 years tied up in the success of WPP. So if WPP does well, I do well, and others in the company do well. If we do badly, we suffer."