Record mogul Tommy Mottola has resigned as chairman and chief executive officer of Sony Music Entertainment.

He is replaced by Andrew Lack, currently president of TV network NBC.

Mr Mottola, who signed Jennifer Lopez and helped guide the careers of Bob Dylan and Bruce Springsteen, is to start his own label in partnership with Sony Music.

"I have been thinking about taking up this new challenge for about a year, and really made the decision to go forward only recently," said Mr Mottola.

His sudden departure, effective immediately, comes after a rocky year for Sony.

Record sales were undermined by the global economic slowdown as well as the swapping of digital music files on the internet.

Contract battles

Times are tough for all record companies Jay Cooper, entertainment lawyer

Sony Music's troubles included a bitter contract dispute last year with US band Dixie Chicks.

And then there was the highly publicised row between Mr Mottola and Michael Jackson, in which the "King of Pop" accused the record boss of being "racist" and "devilish".

But Mr Mottola, 52, was generally regarded as a talent spotter during his 14 years at the helm of Sony Music.

One of his biggest discoveries was his now ex-wife Mariah Carey, whom he married after signing her to his label.

Popular legend has it that Mottola listened to Carey's demo tape in his limo and was so taken by it that he decided to track her down immediately.

"Sony has done well," said entertainment lawyer Jay Cooper.

But he added: "I don't know that they have done spectacularly well.

"Times are tough for all record companies."

Overhaul

Mr Mottola spent much of his last months at Sony Music overseeing a radical overhaul of the talent management business.

He oversaw a marketing deal with soft drinks giant Pepsi , an advertising deal between Celine Dion and Chrysler and bought legend rock band AC/DC's catalogue.

Mr Lack, a veteran TV executive, spent eight years overseeing NBC's news division before winning the top job.

During his time at NBC News, Mr Lack helped create MSNBC, a cable venture with Microsoft.