Wealthy American philanthropist Julian Robertson has given $5 million towards the Christchurch earthquake relief fund.

That amounts to about 5 per cent of the total $100 million that Prime Minister John Key says has been raised globally.

But Mr Robertson is not the mystery donor of another $5 million contribution.

That person is a Kiwi.

And while many regard Mr Robertson as an honorary New Zealander because of his devotion to this country and its people, he is still an American.

Today, Mr Robertson will leave his New York apartment overlooking Central Park and travel to Washington for a black-tie dinner at the New Zealand Embassy, where he will be guest of honour.

He was made an honorary Knight Companion of the New Zealand Order of Merit in the 2010 New Year Honours lists for his contribution to philanthropy and business.

Mr Key will play the role normally performed by the Governor-General and give him the insignia conferring the honour.

It's the equivalent of a knighthood but the honorary title does not come with a "Sir".

Mr Key knew him when he worked at Merrill Lynch in New York and Mr Robertson's Tiger Management investment company was his firm's biggest client.

Mr Robertson's partner in philanthropy over 40 years, his wife Josie, died in June last year of breast cancer.

Together, they gifted to the Auckland Art Gallery 15 works of art (Gaugin, Dali, Picasso, Cezanne and Mondrian among them) worth $115 million - an average of $7.6 million a painting.

The collection will be on show for free for eight weeks over the Rugby World Cup and until October 30.

In an interview with Bloomberg last year, Mr Robertson called New Zealand "the most beautiful place on Earth".

He is thought to have first visited with his wife in the 1970s, then returned to try to write a novel. He spends three months a year at one of the three lodges he owns in Northland, Hawkes Bay and Queenstown.

NZ's Ambassador to Washington, former PM Mike Moore, nominated Mr Robertson for the knighthood, as he had unsuccessfully when Labour was in Government.

Mr Robertson earned a place in Labour history when Trevor Mallard accused National leader Don Brash in the 2005 election campaign of having an American "bagman" and having his campaign financed and run
by Americans.

He didn't actually name Mr Robertson, though it was no secret to anyone - including the Americans, as WikiLeaks shows - that that was who he meant.

Dr Brash denied it and called it a "thundering lie", saying no Americans were involved in the campaign. But leaked emails showed he was considering hiring a couple of Republican operatives on the recommendation of Mr Robertson.

Mr Robertson is a strong Republican supporter. He has given donations to National but he also gave one to Labour MP Dover Samuels for his Te Tai Tokerau campaign.

When Helen Clark was prime minister, Labour moved to outlaw political donations from foreigners abroad.

Mr Robertson appears not to bear grudges, however, hosting Helen Clark to dinner in New York after she moved there to take up the role of head of the United Nations Development Programme.

New Zealander John Hood, the former vice-chancellor of Oxford University, is now the chief executive officer of the Robertson Foundation, which makes large donations in four main areas: education, environment, religion and medical research.

Mr Robertson could not be contacted for comment.