Yesterday a dump of leaked documents from the Heartland Institute — a US-based think tank that pushes a strong climate change denier agenda — revealed the inside workings of the organisation and the funding it receives from tobacco, telecommunications and drug companies.

After Graham Readfearn wrote for Crikey on the leaked documents yesterday, the Heartland Institute overnight released a statement acknowledging the leaks and threatening legal action against media organisations publishing stories based on them. “Some of these documents were stolen from Heartland, at least one is a fake, and some may have been altered,” it said.

According to Heartland the Confidential Memo: 2012 Heartland Climate Strategy document is “a total fake apparently intended to defame and discredit The Heartland Institute”. Much of the reporting in the last 24 hours has focused around this particular document — claims that the Charles G.Koch foundation (set up by oil billionaire brothers David and Charles Koch) donated $200,000 to the organisation, that organisations whose “interests are threatened by climate policies” will be targeted as potential donors and that a curriculum is being developed for school children based on a climate sceptic agenda.

Others question how “fake” the document truly is. DeSmogBlog, the climate news website that originally broke news of the leaked documents and published them all online, outlined four different parts of the alleged fake climate strategy that have been verified by other people or documentation, including the development of a K-12 school curriculum.

But this morning the Charles Koch Foundation released a statement denying it donated $200,000 to the Heartland Institute or that further donations were expected, as the leaked climate strategy memo claimed. Spokesperson Tonya Mullin said:

“It’s unfortunate that those reporting on the matter did not seek the facts as they would have found the Charles Koch Foundation provided $25,000 to the Heartland Institute in 2011 for research in healthcare, not climate change, and this was the first and only donation the Foundation made to the institute in more than a decade. The Foundation has made no further commitments of funding to Heartland.”

In 2010 Greenpeace did an investigation into how the Koch brothers, through their various foundations, funnel money into climate denier organisations. Greenpeace found that between 2005-2008 the Koch foundations donated US $24.9 million to various climate denial organisations (Heartland was not one of them).

But while the Koch brothers may not donate to Heartland, the leaked documents reveal that a very powerful and wealthy donor has donated US$13.7 million since 2006. The mystery donor, referred to throughout the leaked documents as “Anonymous Donor”, has provided up to 60% of donations for the Heartland Institute in the last six years.

He (he is referred to as male throughout the documentation) has already pledged $1 million this year and Heartland projects “that he will give $250,000 more over the course of the year”.

In 2007 his donation of $3.27 million made up 63% of the organisation’s contributions. In 2008 he gave a whopping $4.6 million, which made up 58% of total contributions.

Meaning that during the global financial crisis — and the US presidential campaign — this individual played a very powerful role in keeping Heartland afloat. In 2008 Heartland began its powerful anti-climate change conferences, fronted with well-known sceptics.

Last year the anonymous donor gave $979,000, the lowest amount since 2005. Even still it made up 20% of Heartland’s revenue.

Heartland actively seeks to keep this donor content. “Renewing him each year and keeping him informed and engaged is a major responsibility of the President. We regularly solicite [sic] his ideas for new projects,” it says in the leaked Heartland’s 2012 Fundraising Plan (where the Anonymous Donor has his own section devoted to him).

It seems the donor is predominately interested in the climate sceptic aims of Heartland. “We are extinguishing primarily global warming projects in pace with declines in his giving, and we were careful not to hire staff based on his past generosity,” says the agenda for a 2012 meeting of directors in January.

But apart from that he is male, wealthy and particularly interested in pushing an anti-global warming agenda, not much is known of the donor.

As Leo Hickman in The Guardian points out, he is likely American: “There are few clues about his identity other than he has also personally funded a couple of Heartland’s non-climate projects in Illinois and Wisconsin which might suggest a personal, local interest.”

There’s already been some speculation on the identity of the Anonymous Donor. As Jess Zimmerman writes at Grist:

“Oh man, who could it be? It’s probably another Koch but imagine if it were, like, Karl Rove. Or alternately, imagine if it were Al Gore!”

In the Heartland Institute press release acknowledging the leaked documents, the organisation apologised to donors who had been affected by the leaked documents:

“The Heartland Institute apologizes to the donors whose identities were revealed by this theft. We promise anonymity to many of our donors, and we realize that the major reason these documents were stolen and faked was to make it more difficult for donors to support our work. We also apologize to Heartland staff, directors, and our allies in the fight to bring sound science to the global warming debate, who have had their privacy violated and their integrity impugned.”

Other donors to Heartland must be frustrated about their identity being made public, but the Anonymous Donor has managed to keep his. So far.

Update: this article originally stated that the Anonymous Donor had donated $US8.6 million since 2007. This has been changed to $13.7 million since 2006