Secret footage recorded during an Al Jazeera investigation has revealed senior One Nation figures met with representatives of one of America's richest companies last year to discuss possible political funding.

That company was Koch Industries, a multi-billion-dollar empire run by Charles Koch (and until last year, his brother David).

Together, the Koch brothers (pronounced 'coke') are two of the most powerful people in the United States.

Here's what we know about them.

Charles (left) and David (right) Koch are the eleventh-richest people in the world. ( Facebook )

The Koch brothers are billionaire businessmen

Charles and David are estimated to be worth a whopping $US50.6 billion ($71.3 billion) each and tied for the eleventh-richest person in the world in 2018.

They inherited Koch Industries from their father in 1967 and it's now the second-largest private company in the US (under the food, drink and tobacco giant, Cargill).

The huge conglomerate runs multiple businesses across the world, bringing in annual revenues of up to $US110 billion ($154.8 billion) a year, according to Forbes.

Those businesses manufacture everything from fertilisers and chemicals to toilet paper and carpets.

They are philanthropists and political mega-donors

The Koch brothers have donated large sums of their fortune to various causes over the years, including cancer research and the arts.

But they are also political mega-donors who have channelled billions of dollars into conservative initiatives in America.

Shaun Ratcliff, a lecturer in political science at the United States Studies Centre, said the brothers were pro-business libertarians who funded campaigns for lower taxes, less regulation and free trade.

But what makes the Koch brothers particularly influential in American politics, according to Dr Ratcliff, is their extensive political network.

"They funnel a lot of their own personal money to a number of different organisations that then support conservative causes," he said.

As Dr Ratcliff put it, they've got their fingers in a lot of pies.

They've also got a lot of sway

The Koch brothers have spent millions to help elect like-minded Republicans, but have openly clashed with Donald Trump since his election in 2016.

Most recently they've taken issue with his trade policies.

Donald Trump announced steel and aluminium tariffs on the EU, Mexico and Canada last year. ( Reuters: Carlos Barria )

Just before the midterm elections last year, Koch Industries launched a six-figure digital ad campaign denouncing Mr Trump's tariffs on "steel, solar panels and washing machines".

Charles also wrote a lengthy opinion piece for the Washington Post that advocated for free trade and called on corporate leaders to reject "Trump's tariffs".

This sort of spending has in the past seen the brothers accused of trying to "buy America".

But Mr Trump said he didn't need the brothers' "money or bad ideas".

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So why would One Nation meet with Koch Industries?

According to Al Jazeera's investigation, when Pauline Hanson's chief of staff, James Ashby, and the party's Queensland leader, Steve Dickson, went looking for funding in the US last year, the National Rifle Association (NRA) suggested they meet with representatives from Koch Industries.

Senator Hanson did not attend the trip.

According to Dr Ratcliff, Koch Industries has funded NRA-related initiatives in the past.

During the meeting, however, the company's representatives also said they weren't "naive to the importance of policies in Australia and how they relate here in the US".

"It's not lost on us that the world we operate in is driven by international commodities markets. What you do in Australia has a huge impact," one woman said.

There's no evidence One Nation was successful in its efforts to extract funding from the company.

Covert footage taken during the Al Jazeera investigation showed the two parties discussing the laws and public disclosure requirements in Australia for political donations.

The Koch Industries representatives appeared interested in both the rules and regulations, but also how political donations were viewed "culturally" in Australia.

Watch the second part of the Al Jazeera investigation on Thursday on ABC TV or watch the full documentary on iview.