Dr John Sinclair AO died on Sunday after working for 48 years to protect Queenland's natural environment.

The international reputation of Fraser Island - known to the indigenous Butchulla people as K'gari - was highlighted in 2018 when the Duke and Duchess of Sussex, Prince Harry and Meghan Markle - visited the island as part of their first Australian tour.

Dr Sinclair, born in Maryborough, came to public attention when he formed the Fraser Island Defenders Organisation, known as FIDO, in 1971.

That decade Dr Sinclair took the then-Queensland premier Sir Joh Bjelke-Petersen's government to court for failing to protect the natural environment of Fraser Island.

The two-decade battle left him bankrupt.

But the public attention his conservation bid received paved the way for Fraser Island to become one of the world's most recognisable World Heritage-listed sites.

In an interview with Brisbane Times in September 2017, when he received an honorary doctorate from the University of Sunshine Coast, he described his battle with sand miners as protecting an environment as beautiful as the Mona Lisa.

"The sand miners used to say, 'We are only going to touch 1 per cent of the island',” Dr Sinclair said.

“I used to say, ‘If you are going to scratch 1 per cent of the Mona Lisa, which 1 per cent are you going to scratch?’ ”

In 1976, Dr Sinclair was named as The Australian newspaper’s Australian of the Year.

In 1990 he was selected by the United Nations Environment Program for individuals who made a substantial and significant role in protecting the environment when he was named in their Global 500.

In 1993 he received the internationally respected Goldman Environmental Prize and in 2014 he was appointed in the Order of Australia.

At that time he still spent "seven to eight weeks a year" on his beloved island and remembers doubting he would win and be able to stop logging and sand mining.

“When we lost the first rounds I had second thoughts,” Dr Sinclair said in September 2017.

“But I just thought we’ve got to stick in there because if we just keep battling away, we'll make it so tough the Bjelke-Petersen government would never, ever sacrifice a beautiful place like Fraser Island again,” he said.

His last visit to K'gari was as a guest of the Butchulla people and Premier Annastacia Palaszczuk, when the Duke and Duchess of Sussex visited Fraser Island to include the rainforest island as part of Queen’s Commonwealth Canopy.

Dr Sinclair leaves four sons and nine grandchildren and his partner Su. He died in Brisbane's Wesley Hospital from prostate cancer.

Keith Sinclair, who accompanied his father countless times to Fraser Island, said his father never sought recognition.

"Dad was very much motivated by Fraser Island not being destroyed. And not just Fraser Island, but many other wild places," Keith said on Monday.

He said his father used his training as an economist to highlight the tourism sustainability of Fraser Island, not simply its value as a source of rutile or of logged timber.

"I remember when logging was stopped I said to him, 'Dad, you've won, there will be no more logging, Fraser is safe'," he said.

"And he said to me, 'No. Now we have to stop Fraser Island from being loved to death.' "

Keith said his father was always thinking of the longer-term issues and wrote the first management plan for Fraser Island.

That mean trips to Yellowstone and Yosemite national parks in the US to see how they used boardwalks allowing tourists to visit striking parts of the environment without harming them.

"He tried to understand how they controlled the people so they had an experience of being in a wild place and being somewhere beautiful but not causing any impact," he said.

"That was his intent. How do we do that?"

He said his father's work to protect Fraser Island was an inspiration to modern conservationists.

"It was a conservation battle but he fought it on economic terms," he said.

"He wrote - it might have been in the World Heritage Listing submission - that Fraser Island would ultimately be worth more in tourism that it would be in mining.

"And he estimated some very conservative figures and unfortunately he was wrong. He was out by a factor of 10.

"Now it is still there and worth so much more to Queensland and to the people in terms of tourism than it would ever have been.

"Tourism is repeatable," Keith Sinclair said.

"As long as you look after the place, you can repeat tourism, you can keep taking people back there."

Mr Sinclair's family requested that John Sinclair be remembered by donations to further the wisest possible use of Fraser Island.

A public memorial service will be held in about a month.