Donald Trump has appointed Jared Kushner as a White House senior adviser, which means he'll continue to have a big influence on domestic and foreign policy, particularly Middle East issues and trade negotiations.

You probably already know that he's married to the US President-elect's daughter Ivanka. But there's more to him than that.

Businessman turned political adviser

In some ways, the 35-year-old has a similar story to Mr Trump. Like him, Mr Kushner is a real estate executive who has pushed his family's company into the high-stakes battlefield of Manhattan.

As well as being CEO of Kushner Companies, he's the publisher of the New York Observer newspaper. He'll resign from both of these roles (and divest "substantial assets", according to his lawyer) upon taking his position in the White House.

But while they're both businessmen, Mr Kushner is very different to Mr Trump in other ways. While the President-elect likes to make his voice heard in the media, Mr Kushner is soft spoken and press-shy.

He's also often viewed as more moderate than Mr Trump, but people close to him say he fully bought into the campaign's fiery populist message that resonated with white, working-class voters.

He never publicly distanced himself from Mr Trump's more provocative stances, including the call for a Muslim-immigration ban and his doubts about President Barack Obama's birthplace.

During the election, Mr Kushner was one of Mr Trump's most powerful advisers, and he was deeply involved in the campaign's digital efforts.

He was usually at Mr Trump's side during the election's closing weeks, and since then he's been a leading figure during the transition, working alongside White House chief of staff Reince Priebus and senior adviser Stephen Bannon.

Key voice on foreign policy and the Middle East

Last week, Mr Kushner and Mr Bannon met with British Foreign Minister Boris Johnson.

They have also worked closely on issues related to Israel, including discussions over moving the US Embassy to Jerusalem, and on the Trump administration's response to a United Nations Security Council measure condemning Israeli settlements.

Sorry, this video has expired Dr Carl Rhodes discusses the legality of Jared Kushner's appointment.

Meanwhile, Mr Kushner has played a key role in coordinating Mr Trump's contacts with foreign leaders and has been talking with foreign government officials himself, according to a person with knowledge of the conversations.

His influence isn't limited to foreign policy, either.

He's helped interview cabinet candidates, and he joined other Trump advisers on Monday night for a meeting with House Speaker Paul Ryan on tax reform. As well, he championed the pick of his friend Gary Cohn, the president of Goldman Sachs, as director of the National Economic Council.

In a statement, Mr Trump said Mr Kushner will be an "invaluable member of my team as I set and execute an ambitious agenda".

Is this nepotism?

Mr Kushner's eligibility for the White House could be challenged, given a 1967 law meant to bar government officials from hiring relatives.

But his lawyer Jamie Gorelick has argued that the law does not apply to the West Wing. She cited a later congressional measure to allow the president "unfettered" and "sweeping" authority in hiring staff.

Norman Eisen, who served as President Barack Obama's government ethics lawyer, said there is a "murky legal landscape" regarding the anti-nepotism law.

But he said Mr Kushner appeared to be taking the proper steps regarding the ethics and disclosure requirements for federal employees.

ABC/Reuters