Les Hinton, one of the top executives of Rupert Murdoch's embattled News Corporation media empire, has quit.
Mr Hinton was chief executive of Dow Jones, publisher of the Wall Street Journal. Mr Murdoch said the resignation brought him "much sadness".
Rebekah Brooks - chief executive of the media group's UK newspaper arm, News International - also quit on Friday.
She was arrested on Sunday, the 10th arrest made by police investigating phone hacking by the News of the World.
Mr Murdoch apologised for "serious wrongdoings" by the News of the World, in full-page advertisements signed by him, in Britain's main national newspapers on Saturday.
'An unexpected end'
Mr Hinton led News International from 1995-2007, when the UK's News of the World was hacking phones.
Mr Hinton worked for News Corp for more than half a century after joining Mr Murdoch's business as a cub reporter with the Adelaide News in Australia.
In a statement, Mr Hinton said: " I have watched with sorrow from New York as the News of the World story has unfolded.
"I have seen hundreds of news reports of both actual and alleged misconduct during the time I was executive chairman of News International and responsible for the company.
"The pain caused to innocent people is unimaginable.
"That I was ignorant of what apparently happened is irrelevant and in the circumstances I feel it is proper for me to resign from News Corp, and apologise to those hurt by the actions of the News of the World."
Mr Murdoch shut down the 168-year-old Sunday tabloid last week in response to the phone-hacking scandal, with the loss of 200 jobs.
At the Wall Street Journal, news of Mr Hinton's sudden departure was reportedly greeted by gasps from stunned staff.
In the wake of the phone-hacking scandal, Mr Hinton is the first Murdoch executive to fall on his sword in the US, where the FBI announced on Thursday it was investigating whether the News of the World had also snooped on the phones of 9/11 victims.
Mr Murdoch said in a statement: " Les and I have been on a remarkable journey together for more than 52 years .
"That this passage has come to an unexpected end, professionally, not personally, is a matter of much sadness to me."
The Australian-born media baron added: "I vividly recall an enthusiastic young man in the offices of my first newspaper in Adelaide, where Les joined the company as a 15-year-old and had the rather unenviable task of buying me sandwiches for lunch."
Mr Murdoch's statement added: "Let me emphasise one point - News Corporation is not Rupert Murdoch.
"It is the collective creativity and effort of many thousands of people around the world, and few individuals have given more to this company than Les Hinton."
Earlier on Friday, Mr Murdoch apologised to the family of murdered British schoolgirl Milly Dowler.
The crisis shaking News Corp exploded after it emerged the 13-year-old's mobile phone had been hacked by the News of the World newspaper in 2002.
Allegations surfaced last week that the News of the World had also snooped on senior politicians, the victims of London's 2005 terrorist bombings and the families of dead British soldiers.
On Saturday, a committee charged with monitoring ethics at the Wall Street Journal said that it found no evidence of any wrongdoing.
It also said that it did not believe that Mr Hinton resigned due to anything that occured at the unit of News Corp.
The committee was formed in 2007 when Mr Murdoch bought the newspaper as a way of allaying concerns over its editorial integrity under News Corp.
As Mr Murdoch emerged from a meeting with the Dowler family at a London hotel to tell reporters he was appalled by their ordeal, the 80-year-old was jeered by hecklers.
Also on Friday, UK Prime Minister David Cameron said the resignation of Ms Brooks, who was News of the World editor between 2000-03, had been "the right decision".
This week Mr Cameron appointed a judge to conduct a sweeping inquiry into criminal activity at the paper and in the British media.
Ms Brooks, 43, had been with News International for 22 years, and was also Mr Cameron's friend and neighbour.
She has been replaced by Tom Mockridge, a New Zealander who was in charge of News Corporation's Italian broadcasting arm.
Following Mr Hinton's departure, Dow Jones President Todd Larsen will report to News Corp Chief Operating Officer Chase Carey, the company said.
Earlier this week, the scandal prompted News Corp to abandon a multi-billion dollar bid to take full control of British pay-TV operator BSkyB.