Google is losing a top executive in charge of building its display advertising business, an area where the company is playing catch-up to rivals.

David Rosenblatt, Google’s president of global ad sales, is leaving May 15. Henrique De Castro, a sales executive in Europe, will replace him.

Rosenblatt was the chief executive of DoubleClick in 2007, when Google agreed to buy it for $3.1 billion. He stayed with the company after the deal closed in 2008.

Later that year, Google gave him a bigger title and put him in charge of its global efforts, presumably to keep him happy.

Google has been trying to come up with a solid second act after the success of its paid search business.

Rosenblatt’s departure follows the loss of Tim Armstrong, Google’s vice president of the Americas, who left last month to lead Time Warner’s struggling AOL division.