Donald Trump announced Tuesday that the world's richest man, Elon Musk, will lead a new US government efficiency group tasked with cutting federal waste, as the Republican president-elect added a series of seasoned figures and hardliners to his incoming administration.

Musk became a key ally to Trump during his campaign, reportedly spending over $100 million to help the Republican win and repeatedly boosting Trump's candidacy on X, the platform he owns.

Trump said Musk and another stalwart ally, businessman Vivek Ramaswamy, would lead a "Department of Government Efficiency ('DOGE')" a tongue-in-cheek reference to an internet meme and cryptocurrency.

"Together, these two wonderful Americans will pave the way for my Administration to dismantle Government Bureaucracy, slash excess regulations, cut wasteful expenditures, and restructure Federal Agencies," Trump said in a statement.

He said the department "will provide advice and guidance from outside of Government," a move that could allow Musk to avoid disclosing his financial holdings.

In a post on X, Musk said the department's actions will be published online "for maximum transparency" and will include a "leaderboard for most insanely dumb spending of your tax dollars."

"This will be both extremely tragic and extremely entertaining," Musk wrote.

Trump, 78, is set to make a triumphant return to Washington on Wednesday, meeting President Joe Biden in the Oval Office.

He may also visit the US Capitol where his party has won a narrow majority in the Senate and is poised to retain control of the House of Representatives.

With just over two months until he takes office, Trump is moving quickly to consolidate an extraordinary comeback.

Governments worldwide are scrutinizing Trump's picks for signs of how closely the incoming administration will stick to his promises of an isolationist foreign policy, harsh crackdowns on illegal immigration, and persecution of people he perceives as enemies.

- Hardliners -

Late Tuesday, Trump named military veteran and Fox News host Pete Hegseth as his incoming defense secretary.

"With Pete at the helm, America's enemies are on notice -- Our Military will be Great Again, and America will Never Back Down," he said in a statement.

Meanwhile, US media reported that Florida Senator Marco Rubio would be nominated to the key position of secretary of state.

Trump separately named congressman Mike Waltz, a former special forces officer, as his incoming national security advisor.

Waltz has hawkish views on China but is not considered isolationist, despite desire in some Trump circles for the United States to retreat from foreign engagements and cut obligations to allies like NATO.

Trump also announced he was choosing his former director of national intelligence John Ratcliffe to lead the Central Intelligence Agency.

On the domestic front, Trump has signaled he will support his extreme election campaign rhetoric aimed at stirring fear and anger against illegal immigrants ahead of promised mass deportations.

Among his appointments are South Dakota Governor Kristi Noem as secretary of homeland security, veteran hardline immigration official Tom Homan as "border czar," and Stephen Miller -- author of Trump's so-called "Muslim ban" immigration policy -- as his powerful deputy chief of staff.

Trump has also picked Lee Zeldin to head the Environmental Protection Agency, with a mandate to slash climate and pollution regulations.

New York congresswoman Elise Stefanik, a fierce Trump ally and pro-Israel stalwart, got the nod for UN ambassador, Trump's transition team said.

Another fervent pro-Israel figure, former Arkansas governor Mike Huckabee, was named as ambassador to Israel.

- Return to the Oval -

Biden's Oval Office invitation restores a presidential transition tradition that Trump dismissed when he lost the 2020 election, refusing to sit down with Biden or even attend the inauguration.

By the time Trump left the White House on January 20, 2021, he had also been repudiated by many in his own party for having encouraged a mob to assault the US Capitol.

The period of disgrace soon evaporated, however, as Republicans returned to Trump's side, recognizing his unique electoral force leading the far-right movement that has now swept him back to power.

While many of his cabinet nominations require approval by the Senate, Trump is trying to bypass that oversight by forcing through so-called recess appointments.