The founder of world’s biggest advertising agency WPP, Martin Sorrell, has stepped down as its chief executive following allegations of personal misconduct through misuse of company assets. The resignation came a week after the agency launched an independent investigation into the allegation. The company’s board expects the findings of the probe to be ready by next week. Sorrell, 73, said he was sad to leave WPP which had been his passion for over three decades. However, WPP and its future is more important to him, he told the staff. He denied any wrongdoing adding that the company had to investigate after the allegation surfaced earlier this month. Roberto Quarta, the WPP chairman, will act as the CEO until a replacement for Sorrell can be found. Sorrell acquired the shell company, Wire & Plastic Products PLC, in 1985 and turned it into a marketing services group in 1986. The company currently employs more than 200,000 people in some 3,000 offices, across 112 countries.