Since campaigning for Trump -- with such enthusiasm that Musk literally jumped in the air at a rally -- Musk has been a near-constant presence at Trump's side.

The Tesla and SpaceX CEO has joined telephone calls with world leaders and dispensed advice on personnel choices both directly and publicly through X, the social media platform he bought.

In between his constant postings of memes of himself and Trump, Musk has even embraced a title suggested for his role: "First Buddy."

When the president-elect triumphantly returned to Washington on Wednesday, tagging along aboard his plane was Musk, the world's richest person, who appears to have spent most of the week since the election hobnobbing at Trump's Florida estate, Mar-a-Lago.

Musk, trading his Silicon Valley bro sweatshirts for a crisp and somber black suit, was given a front-row seat among Republican House lawmakers who gathered to hear the president-elect.

"Elon, you've been so good," Trump said, as the elected representatives offered Musk a standing ovation, according to footage posted by a congressman.

On Tuesday, Trump appointed Musk and another billionaire, former Republican presidential contender Vivek Ramaswamy, to a new "Department of Government Efficiency" tasked with trimming down Washington bureaucracy.

Musk, who sacked 80 percent of Twitter's workforce when he bought it and rechristened it as X, vowed in an announcement to "send shockwaves through the system, and anyone involved in government waste."

Musk has also offered advice well outside of any defined lane for him.

He called for the appointment of the president-elect's daughter-in-law Lara Trump to a US Senate seat expected to open up in Florida should Marco Rubio become secretary of state.

Musk -- and not career diplomats, as would be customary -- reportedly joined Trump in calls with the leaders of Turkey and Ukraine, where Musk's Starlink has provided a vital source of communication during the war.

He also has taken to X while advising Trump to back efforts to defeat Canadian Prime Minister Justin Trudeau.

- Trump's perilous inner circle -

The South African-born Musk, who controversially ran a $1 million-a-day sweepstakes in swing states in a clear bid to attract Trump voters, has so far managed to avoid blowback from the mercurial president-elect.

Trump has gone so far as to suggest he would put aside some of his climate skepticism and back electric cars due to Musk.

The president-elect was said to fume after a first-term consigliere, far-right political strategist Steve Bannon, appeared on the cover of Time magazine and was described as the "second most powerful man in the world."

Trump eventually fired him and nicknamed him "Sloppy Steve."

Musk, whose Tesla cars had been status symbols for wealthy liberals, has also quickly become a lightning rod for criticism from Democrats.

Senator Elizabeth Warren mocked the new initiative of Musk and Ramaswamy, writing on X that the effort for efficiency was "off to a great start with split leadership: two people to do the work of one person."

Until the latest election, Musk said he voted for Democrats for president, including Joe Biden.

The turning point, according to a Wall Street Journal report, was when Biden invited automaker executives to the White House but snubbed Musk because Tesla, unlike the Detroit Big Three, is not unionized.

Whatever the causes, Musk's political transformation has paid off with access unimaginable with most presidents.

On Election Night, a beaming Trump gathered his family together for a picture at Mar-a-Lago. His wife Melania was missing but, at Trump's urging, into the picture came Musk, one of his dozen children in his arms.