Zain Raj, head of Epsilon Agency Services, is exiting the company at the end of September.
Mr. Raj arrived at the data and direct-marketing behemoth via the $460 million acquisition of Hyper Marketing just under a year ago.
In a memo Friday afternoon to employees, CEO Bryan Kennedy said: "Zain has been an integral part over the last year of shepherding HMI into the Epsilon business, as well as helping to craft and communicate the integrated point of view for Epsilon's go-to-market strategy and positioning."
He added: "Zain has decided to leave the company in order to devote more time to finishing his next book, be involved in causes he supports and to spend more time with his family before he embarks on his next adventure. I'm grateful for the contribution and leadership Zain has provided to Epsilon. While we are disappointed to see him go, we wish Zain the very best on his new journey."
The company had no comment regarding Mr. Raj's departure, but according to one person familiar with the matter, the move could spark a broader reorganization of Epsilon's marketing services unit.
Prior to being acquired by Epsilon, Zain was CEO of Hyper Marketing, a large privately held agency, and before that was president-CEO at SolutionSet MediaWhiz Partnership. He also served as North American CEO of Euro RSCG Discovery, the digital, CRM, data and analytics arm of EuroRSCG Worldwide, now known as Havas Worldwide.