Brian Lesser, North American CEO of WPP's GroupM media buying shop, is joining AT&T to lead a new advertising and analytics unit. He'll report to CEO Randall Stephenson.

Brian LesserBrian Lesser

“Brian is a terrific executive and one of the best there is in harnessing technology and data to create targeted advertising,” said Stephenson in a statement. “Once we complete our acquisition of Time Warner Inc., we believe there is an opportunity to build an automated advertising platform that can do for premium video and TV advertising what the search and social media companies have done for digital advertising.”

Lesser noted that advertising "is evolving from broad messages delivered through traditional media channels, to customized, individual content coordinated across all connected devices."

He said AT&T "has amazing assets for creating engaging advertising experiences for consumers."

GroupM had worked for AT&T for a number of years, but lost the business last year to Omnicom.

Kelly Clark, GroupM's global CEO, will assume Lesser's duties until a successor is found.