Commenting on the Mel Karmazin story this morning, Howard Stern announced on his radio show that with the resignation of Karmazin from Viacom that Stern, himself, was as good as gone. “There’s no one left in this company with the backbone to stand up to the FCC,” said Stern acknowledging Karmazin’s ability in the past to run intereference for him. “Mel leaving is as devastating as it gets,” Stern said. “It’s like losing your father. This is the guy who had my back.”

New York- The media conglomerate Viacom Inc. announced today that Mel Karmazin was resigning as president and chief operating office for “personal and professional reasons.”

He is succeeded by Tom Freston and Leslie Moonves, who have been named co-presidents and co-chief operating officers.

According to a statement posted on the company’s Web site, they will become the leading candidates to take over as chief executive officer from Sumner M. Redstone, 80, who has indicated he will step down from that role within three years.

In the announcement, Mr. Redstone said he was “very excited” about working with Mr. Freston and Mr. Moonves, and that “we very much regret Mel’s decision to resign and we wish him well.”

Mr. Feston is chairman and chief executive officer of MTV Networks. Mr. Moonves is chairman and chief executive officer of CBS, overseeing all its programming, sales and management operations.

Mr. Karmazin said in the announcement, “After more than 20 years with the company, for personal and professional reasons, I have decided to leave Viacom and pursue other challenges. Viacom is performing exceptionally well with leadership positions in all of its positions.”

But Mr. Karmazin’s resignation, after more than 20 years with the company, comes against a background of tensions between Mr. Redstone and Mr. Karmazin, and between Mr. Karmazin and Mr. Redstone’s daughter, Shari, 50, who had planned to play a greater role in the company.

Her intention to become more involved was signaled last month when she purchased an elegant apartment on Manhattan’s Upper East Side and said she planned to spend a third of her time at Viacom next fall. Until then she had focused her attention on running National Amusements, her family’s privately held theater chain in Boston.

Ms. Redstone does not have a formal title at the diversified media company, but it was well known that Mr. Karmazin and Ms. Redstone did not get along well, although Ms. Redstone said of Mr. Karmazin last month, “We get along well.”

After Mr. Karmazin and Mr. Redstone merged CBS and Viacom in 1999, Mr. Karmazin insisted the Redstone children – Shari and her brother, Brent, who was then on the Viacom board – stop attending some divisional meetings.