Brian O'Kelley, founder and CEO of AppNexus Inc., will move away from day-to-day operations and work in an advisory role, following AT&T Inc.'s acquisition of the company, people familiar with the matter told The Wall Street Journal.

“Brian is a leader’s leader, and I appreciate him setting up a fantastic team at AppNexus that will help lead Xandr to the next level," Brian Lesser, head of AT&T's new advertising and analytics unit Xandr, reportedly said in the email.

Former AppNexus CFO Jonathan Hsu and former Chief People and Legal Officer Nithya Das are also moving to advisory roles.

AT&T agreed to buy AppNexus in June for an undisclosed sum and closed the transaction in August.