New York, United States | Rudy Giuliani guided New York through its darkest days after 9/11 as the Big Apple's mayor with his signature tough-guy style, but he hasn't held office in 15 years. 

Now, the man once known as "America's Mayor" is reportedly atop the list of hopefuls to be the country's next secretary of state, in what would be a stunning political comeback to reward his loyalty to Donald Trump during a brutal presidential campaign.

The 72-year-old Giuliani's resolve during the aftermath of the worst terror strikes on US soil remains the crowning professional achievement for the Italian-American Brooklyn native, who tirelessly reassured a devastated city.

The image of a tough-talking, never-say-die champion of ordinary New Yorkers was one Giuliani first cultivated as a crime-fighting former federal prosecutor, dealing blows to the mob in the 1980s. 

He burnished that credential during his two terms at city hall, when the murder rate plummeted and he offered his staunch support to the New York Police Department.

Giuliani thus became a law-and-order hero, and decided to try his luck on the national stage, vying for the Republican presidential nomination in 2008.

Though he led in the polls early on, he withdrew from the race before it really began after learning he had prostate cancer.

Most of his policy prescriptions at the time sound a lot like what Trump promised on the campaign trail this time around: an end to illegal immigration, tax cuts, a reduction in the number of abortions, and cleaning up Washington.

At the time, he did not flinch about abandoning positions he had held in the past that were far less conservative -- another common thread with his potential new boss. 

Giuliani had previously supported gay marriage, abortion rights and tougher gun controls. The onetime Democrat became an independent in the 1970s and then joined the Republican Party in the 1980s.

- 'Unconventional' pick -Born on May 28, 1944 in East Flatbush to first-generation Americans, Giuliani is the consummate New Yorker. He studied philosophy and law in the city, earning degrees from Manhattan College and New York University's law school.

When Trump -- himself a life-long New Yorker -- announced his bid for the US presidency, Giuliani immediately teamed up with the Manhattan property mogul.

The men attended each other's third marriages -- in 2002 for Giuliani, and in 2005 when Trump married Melania.

Giuliani, long off the Republican Party's national radar, didn't have much to lose in embracing Trump's outsider White House bid.

During the campaign, he was a top surrogate for Trump, appearing often on news programs to get out the Republican's message. But he also raised hackles with his sometimes incendiary comments about Democrats.

That loyalty is now on the verge of being rewarded -- with a top cabinet spot at the State Department, or perhaps elsewhere.

"It would be somewhat an unconventional appointment but this is obviously an unconventional candidate and an unconventional campaign," said Daniel DiSalvo, a professor of political science at the City College of New York-CUNY.

Though he is well versed on security and the US fight on extremism, he is less experienced in the world of diplomacy, for which his brash, no-holds-barred speaking style might not seem well-suited.

He certainly has fewer bona fides than current Secretary of State John Kerry or his predecessors Hillary Clinton (Trump's vanquished rival for the White House), Condoleezza Rice or Colin Powell, DiSalvo said.

And his nomination is not a done deal, with CNN reporting, citing a source familiar with Trump's transition talks, that Giuliani's business ties -- including lobbying for Citgo, the US subsidiary of Venezuela's state oil company PDVSA  -- could complicate matters.

Giuliani did express a few opinions about foreign policy during the campaign and even before, most of them all in line with his usual firmness.

On Monday, at a forum hosted by The Wall Street Journal, he spoke about his vision, putting the fight against the Islamic State group atop his agenda -- a subject firmly in his wheelhouse -- and saying Russia was not a military threat to America.

Giuliani is an indefatigable champion of Israel, a hardliner with respect to the Palestinians, and a critic of the nuclear deal with Iran negotiated by the outgoing administration of President Barack Obama.

His relative inexperience on foreign policy and distance from the Republican party brass could paradoxically play to his advantage, DiSalvo said.

"Trump, in some ways, ran an insurgent campaign that opposed much of the current establishment of his party," he told AFP.

"So in that respect, when it comes to nominating people, he had to reach out beyond people who'd been close to power in the current national scene for the last few years."