Keith Tannenbaum is the Chief Executive Officer of Atlantic Net, the primary insurance company providing revenue to Princeton-Plainsboro Teaching Hospital. He appears in the Season 6 episode 5 to 9. He is portrayed by actor Patrick St. Esprit.
When Cuddy was in a fee dispute with Atlantic Net, she wondered if she should go over the head of their chief negotiator Eli Morgan after she threatened to cut off their contract. However, she didn't know where to find Tannenbaum until she turned to her then boyfriend Lucas Douglas.
Lucas found out where Tannenbaum was having lunch and confronted him about how little the fee hike they were asking would actually cost his company, and she pointed out she had the most innovative diagnostic department in the country. She also threatened to cut off the contract, noting that this would be adverse publicity for Atlantic Net. However, Tannenbaum said he didn't care about negative publicity as long as he had money and went back to his lunch.
Cuddy went ahead and announced the cancellation of the contract. However, when no settlement was forthcoming, she went to resign. However, she missed an elevator and found Morgan coming to see her that Tannenbaum had instructed him to agree to her fee demands.