Nick Robertson, the founder and chief executive of online fashion retailer Asos is to stand down after 15 years, the company has announced.
Mr Robertson is stepping down with immediate effect but will remain on the board as a non-executive director, Asos said.
He is succeeded by Nick Beighton who joined Asos in April 2009 as chief financial officer.
Mr Beighton's appointment was widely expected.
Mr Robertson founded Asos - or As Seen on Screen because its garments were copies of clothes worn by celebrities - in 2000 at the height of the dot.com boom.
The company quickly expanded introducing more fashion ranges and a year later it floated on the Alternative Investment Market (Aim) with a value of £12m. The company has grown into a global operation worth £6bn in the last 15 years with offices and warehouses in North America, Europe and Asia.
However, Asos has faced a difficult 18 months. In March, it reported a 10% fall in first half profits as a strong pound, a large investment programme and price cuts took their toll.
The company reported pre-tax profits of £18m for the six months to 28 February, down from £20.1m a year earlier.
A tumultuous 2014 also saw a warehouse fire at one of its largest distribution centres forcing Asos to suspend trading.
Asos chairman Brian McBride thanked Mr Robertson for his extraordinary achievement in building up the online retailer from a small fashion start-up in 2000 to the business it is today.
He added that Mr Beighton had "unique experience" of the company built over the last six years, equipping him to drive Asos to become "the world's leading online fashion retailer for twentysomethings".
In April Asos announced it had appointed Helen Ashton as chief financial officer, succeeding Nick Beighton in the role. Mrs Aston started with the company on Tuesday.