Dan Akerson arrives at General Motors as CEO with the same mandate given his predecessor just eight months ago: bring new leadership to an automaker still struggling with the legacy of its government bailout.

Akerson, 61, replaces Ed Whitacre as of September in an abrupt shake-up GM announced just a day before it had planned to file for a politically charged stock offering expected to be one of the largest ever.

The suddenness of Whitacre's departure -- coming just a day after a meeting of the top U.S. automaker's board and announced at an improvised teleconference for reporters and financial analysts -- stunned insiders.

GM's financial advisers, who had spent weeks preparing an IPO filing for U.S. securities regulators, scrambled to rewrite complicated paperwork to take Whitacre out and put Akerson in, one person with direct knowledge of the private process said.

Whitacre, who served as CEO at AT&T and steered it through a series of key mergers, remains GM chairman until the end of the year. He had been expected to quit after guiding GM through an IPO to reduce the U.S. government's 61 percent ownership stake.

Just a week ago, Whitacre, 68, said he had not given any thought to resigning. Everybody knows at my age I'm not a real longtimer, he told reporters.

A lanky Texan who confessed to feeling lost in Detroit and commuted home by plane to San Antonio on weekends, Whitacre had become the face of GM's turnaround and starred in TV commercials meant to mark its return from bankruptcy.

At GM, Whitacre became famous for spurning the PowerPoint presentations that had become a symbol of the slow decision-making process at the 102-year-old automaker.

After GM's top executives were blasted for being out of touch and riding to their offices at Detroit's Renaissance Center on a private elevator, Whitacre took pains to mix with workers, showing up unannounced in offices and factories.

But Whitacre's hands-off style of delegating also left him appearing sometimes out of touch and at odds with the Obama administration, which wants to see a successful IPO as early as November.

Last week Whitacre said GM was weeks away from an IPO filing, a statement that puzzled staff who were almost finished with the needed work.

QUIET REPUBLICAN AS IPO PITCHMAN

Akerson, who will take over from Whitacre and lead GM's road show, becomes GM's fourth CEO in 18 months.

A quiet and private executive, Akerson will also face the pressure of becoming the face of GM in an industry where the CEO is often called on to be the biggest salesman.

Like Whitacre, Akerson had a long career in the tightly regulated telecommunications industry. He also has a history of dealmaking as head of buyouts at private equity firm The Carlyle Group.

Akerson became head of global buyouts at Carlyle last July, and was designated by the Treasury Department to serve on the GM board in July 2009 after the automaker emerged from its government-supported bankruptcy.

Analysts said Akerson heads off potential investor concern about executive succession.

A former U.S. Navy officer who served on a destroyer from 1970 to 1975, Akerson supported fellow Navy veteran and Republican John McCain for president.

In 2008, Akerson and his wife donated $80,800 to the Republican Party and its candidates, and nothing to the Democrats or now-President Barack Obama, according to the Center for Responsive Politics in Washington.

The Obama administration has repeatedly said that it chose its representatives on GM's board, including Akerson, for their qualifications without considering their politics.

'NEVER AN IN-YOUR-FACE CEO'

Akerson began driving a black Cadillac CTS about a year ago, around the time the White House asked him to join the GM board.

He joined Carlyle in 2003 and was involved in some of the firm's biggest deals, including buyouts of energy firm Kinder Morgan and media company Nielsen.

Earlier, Akerson was a protege of entrepreneur Craig McCaw, a major backer of both XO and Nextel Communications, both of which Akerson headed.

He was never an in-your-face CEO, said Jeff Kagan, an independent telecom analyst. This is an aggressive businessman, but he's very quiet.

At Nextel, Akerson was known for taking charge of complicated engineering meetings, for his quiet manner and for his ruthless focus on the bottom line.

When he took his chief spokesman out to lunch, Akerson would head to his favorite Scottish restaurant, McDonald's, said Daisy Khalifa, who worked with Akerson at Nextel.

Akerson lacks one quality analysts credit with giving Ford Motor Co Chief Executive Alan Mulally a leg up as an outsider -- experience in manufacturing.

Ford hired Mulally away from Boeing Co in 2006 and as CEO, Mulally has been credited with leading a surprising turnaround of the No. 2 U.S. automaker.

But GM former Vice Chairman Bob Lutz, a legendary car guy in Detroit, said that lack of experience won't stop Akerson.

Like many strong leaders, he has equally strong opinions, Lutz said, adding that he would have to listen to the new layer of management Whitacre has put in place.

If he can do that, GM will face a very bright future under his leadership, he said.

(Reporting by David Bailey, Bernie Woodall and Ben Klayman in Detroit, Megan Davies, Soyoung Kim and Sinead Carew in New York, David Lawder in Washington. Editing by Robert MacMillan)