Billionaire Elon Musk took a wild gamble backing Donald Trump's White House candidacy, but the bet has paid off -- at least for now -- with the US president-elect handing him an outsized role to overhaul the government.

Musk said before the election that a new "Department of Government Efficiency" would slash $2 trillion from the federal budget -- a big promise echoing his sky-high business ambitions that have made him the world's wealthiest person.

With few details released, questions remain about how Musk will lead the agency, including how he will juggle his new role while managing SpaceX, Tesla, and his other ventures, including X.

With Musk's businesses all having varying degrees of interactions with US and foreign governments, his new position also raises concerns about conflict of interest.

In his announcement, Trump said that Musk and another wealthy ally, Vivek Ramaswamy, would co-lead the new initiative and "provide advice and guidance from outside of Government."

Endorsing a Republican candidate and helping propel him to victory was a shift towards politics for Musk.

The 53-year-old South African-born entrepreneur rose to fame as the face of the nascent electric vehicle industry and has frequently expounded on the threats of climate change.

When Trump pulled the United States out of the Paris Climate Accords in 2017, Musk resigned from two presidential advisory councils in protest.

Years later, Musk has become Trump's most prominent celebrity endorser, leaning fully in to get him and his "Make America Great Again" agenda back in the White House.

Musk reportedly spent over $100 million to help Trump get elected, a massive sum, though a tiny fraction of his estimated $300 billion fortune.

He also used his influence on X, where he has more than 200 million followers, to push pro-Trump messages, as well as inflammatory disinformation about illegal immigration and voting.

However, it remains to be seen how two notoriously egocentric personalities like Musk and Trump will get along in the long term.

Illegal immigration

Born in Pretoria on June 28, 1971, to an engineer father and a Canadian-born model mother, Musk left South Africa in his late teens to attend Queen's University in Ontario.

He transferred to the University of Pennsylvania after two years and earned bachelor's degrees in physics and business.

After graduating from the Ivy League school, Musk abandoned plans to study at Stanford University in California.

He instead dropped out and started Zip2, a company that made online publishing software for the media industry.

During the 2024 campaign -- during which illegal immigration was once again Trump's key issue -- reports resurfaced that Musk had likely violated his visa when he left Stanford.

Musk banked his first millions before the age of 30 when he sold Zip2 to US computer maker Compaq for more than $300 million in 1999.

Musk's next company, X.com, eventually merged with PayPal, the online payments firm bought by internet auction giant eBay for $1.5 billion in 2002.

After leaving PayPal, Musk embarked on a series of ever more ambitious ventures.

He founded SpaceX in 2002 -- now serving as its chief executive officer and chief technology officer -- and became the chairman of electric carmaker Tesla in 2004.

After some early crashes and near-misses, SpaceX perfected the art of landing booster engines on solid ground and ocean platforms, rendering them reusable -- a major advancement in the field.

Musk has said he wants to make humans an "interplanetary species" by establishing a colony of people living on Mars.

To this end, SpaceX is developing a prototype rocket, Starship, which it envisages carrying crew and cargo to the Moon, Mars and beyond.

The spaceship, the world's largest, has already completed several tests, most recently a successful "catch" of a booster.

Musk, who holds US, Canadian and South African citizenship, has been married and divorced three times: once to the Canadian author Justine Wilson and twice to British actress Talulah Riley. He also dated the artist and singer Grimes. He has had 12 children, one of whom died in infancy.

Pete Hegseth, nominated

On Tuesday night, Trump also nominated Pete Hegseth, a former U.S. Army major and current host of Fox News, the favorite network of conservatives in the United States, as secretary of defense.

"With Pete at the helm, America's enemies are on notice: our military will be great again and America will never go backwards," Trump said in a statement. He is "tough, smart and a true believer in 'America First,'" he said earlier on social media.

© Agence France-Presse