Ralf Specht, who founded creative agency Spark44 with Jaguar Land Rover in 2011, has stepped down from the business.
A Spark44 spokesperson confirmed his departure and said he had decided by mutual agreement to make way for new leadership.
Alex Buck, who joined as independent chairman in January, takes over as interim chief executive with immediate effect. He has three decades of experience in the communications industry, including as chief executive of Peter Schmidt Group, part of BBDO.
"The board and Ralf have mutually agreed that as Spark44 enters into the new decade that this is the appropriate time to hand over CEO responsibilities to a new leadership taking the company on to the next stage of the journey," Buck said.
Specht founded Spark44, the industry's first agency/client joint venture, together with four partners and JLR in 2011 and has overseen its expansion from a start-up to a multi-client global agency spanning 19 offices. Clients now include Allianz, Harley-Davidson and Tetley.
Spark44 said Specht, who in January 2018 was promoted from chief operating officer to chief executive, had been "instrumental" in driving Spark44’s reputation and growth.
"We thank Ralf for his commitment, passion and incredible contribution to Spark44 from the first days in 2011 until today. We wish him only the best for the future," Buck added.
Specht said: "I am leaving the agency that I had the privilege to be a co-founder of and I appreciate Jaguar Land Rover's commitment and courage to set up such a unique and radical agency model.
"I have only very fond memories of outstanding Spark44 people from around the world that I had the pleasure to work with during the past nine years."