Leonard Casley, the founder of the micro-nation of Hutt River in Western Australia's Mid West, has died aged 93.

Key points: Prince Leonard died after entering hospital over the weekend with a lung infection

Prince Leonard died after entering hospital over the weekend with a lung infection He handed his son the reins to Hutt River in 2017 after more than 40 years in charge

He handed his son the reins to Hutt River in 2017 after more than 40 years in charge He previously called his time in the role "a very interesting intellectual challenge"

Known as "Prince Leonard", he decided to secede from Australia and form the principality of Hutt River in 1970 after a stoush with the State Government over wheat production quotas.

He was locked in a legal battle with the Australian Taxation Office (ATO) for a number of years, but in 2017 was ordered along with his son Arthur to pay $3 million in income tax.

Prince Leonard was admitted to hospital over the weekend with a lung infection and died early Wednesday morning.

He had been suffering emphysema and abdicated to his son Graeme at a ceremony two years ago.

Prince Leonard abdicated to his son Graham two years ago. ( ABC News: Eliza Borrello )

"It certainly would be nice to be able to continue, but again, you've got to be able to realise that we've all got our own period of life," Prince Leonard said at the time.

"I'm very happy to be handing it over to Prince Graeme, because I know he's very able and capable."

Reflecting on more than four decades in the role, Prince Leonard said the position had been both rewarding and difficult.

"It has been a very interesting intellectual challenge," he said.

'He was a joking man, a self-made man'

Prince Graeme said while it was a sad time, he was proud of his father.

"People come to the end of their lives; you know it is going to happen," he said.

"But what a life the man lived … what one man has achieved taking on the Western Australian Government, the Australian Government and the British Government and holding a country for nearly 50 years — incredible."

He said he was also a loving father of seven children, a grandfather of 22 and great-grandfather of 33.

"He was a joking man, a self-made man and had that dry, sly humour that many Australians have from that era. He would issue a joke with a deadpan straight [expression].

Prince Graeme said he would continue his father's fight to hold his own country.

"We have seen the sacrifices, we have seen the endurances. The family are all behind us and we will continue that," he said.

"I have been the sovereign for two years, I was very lucky that Dad was right there behind me and I could ask him lots of questions.

"He was very sharp, lucid right till the very last few hours."

How a wheat row led to a micro-nation

Hutt River, about 500 kilometres north of Perth in WA's Mid West, is not legally recognised by the Australian Government.

It came about when Leonard Casley moved from his farming and mining interest near Westonia to another farming property, north of Northampton.

Prince Leonard had been suffering from emphysema in the years before his death. ( ABC News: Eliza Borrello )

On April 21, 1970, he proclaimed secession from the state of WA. Later, when asked why, he pointed to the row over wheat quotas.

"That's in '69 when the states all brought in wheat quotas and the wheat quotas [were] brought in at the insistence of the Australian government," he said.

"They were giving a home guaranteed price for wheat farmers and it was up for renewal and the government was concerned the farmers might over produce."

"For 20 years before, we had been producing 13,000 acres of wheat and when we planted in '69 we knew the 10 per cent reduction was coming … and they gave us a quota the equivalent of 100 acres."

Pastoralists and Graziers Association of WA president Tony Seabrook paid tribute to Prince Leonard, saying he challenged the status quo.

"There was an acceptance in those days that you grew your wheat and the Government underwrote the sale of that wheat, so you got paid at harvest time and then the rest came through in dribs and drabs," he said.

"Quotas were a serious imposition. It left a lot of growers with a very limited amount of grain they were able to legally deliver into the system and to have grain beyond that so-called quota, as it was, was undeliverable. You had to keep it on farm and he was incensed by that.

"I think that was the beginning of what became his fiefdom, his kingdom — the fact he wanted to be independent from the controls of government telling him what to do.

"So he challenged the bureaucracy of the day and he gave a lot of people a lot of food for thought."

Mr Seabrook described Prince Leonard as "larger than life".

"One day he was a wheat farmer, doing what the rest of us do, getting covered in dust and chaff, and the next day he was a prince," he said.

"You don't find a lot of people today in our society now that are prepared to differentiate themselves with the daring and the dash that he did.

"I don't know that he changed the world but he certainly added a lot of colour to it."

Tax woes, war calls and tourist trips

Hutt River has long been pursued by the Australian Taxation Office (ATO).

Prince Leonard was recently ordered to pay $3 million to the tax office. ( ABC News: Sarah Taillier )

In 1977, following repeated demands for payments from the ATO, the province declared war on Australia, but withdrew this several days later.

The 2017 judgment from the Supreme Court ordering Prince Leonard and his son to pay $3 million came after the ATO demanded they pay income tax for the eight financial years between June 2006 and 2013.

Hutt River attracts tourists from around the globe who make the pilgrimage to have their passports stamped and purchase the local currency, the Hutt River dollar.

Prince Leonard, a self-described mathematician and physicist, had privately published a number of research papers and books, and developed an educational shrine dedicated to his wife, Princess Shirley, who died in 2013.