"IF I had put as much energy into a commercial venture as I have into this, I would have been a pretty rich man," said Jim Cronin shortly after the opening of Monkey World.

The comment encapsulated the drive, passion and selflessness of the man who was to become one of Britain's most cherished conservationists. Scientist, campaigner, even TV star, Jim, a charismatic New Yorker, was irrepressible.

Monkey World spokesman Jez Hermer said last night that staff had been told of Jim's death. His illness had been known about for seven or eight weeks.

He said: "Jim was determined he would get over it and return to tell them his story himself. Sadly that wasn't the case.

"The staff were briefed last week that he had serious liver cancer and the prognosis wasn't good but at that stage we were all hoping he would pull through."

He said Jim was very much the character people saw on the TV series Monkey Business, which brought Monkey World to a worldwide audience.

"His primary aim was to rescue and rehabilitate apes that had been held in captivity. He was incredibly passionate," he said.

"You would never meet anybody more passionate about a subject."

The establishment and subsequent success of Monkey World was the result of extraordinary dedication.

Twenty years on and animals are still being rescued from across the globe and whisked away to Dorset to be cared for.

Born to Irish-Italian parents in New York in 1952, Jim began his career as a removals man.

But an accident while moving a grand piano left him with his leg in traction and prompted the career change that shaped his life.

He took up a job in the Bronx Zoo, mainly looking after the primates, and moved to Britain in 1980 to take up a position at Howletts Zoo.

Here, Jim set up a primate breeding programme and despite a self-confessed lack of academic qualifications, his methods were widely admired.

In 1985, Jim spelled out his vision for a monkey conservation wildlife park near Wool. And having convinced the council of the park's worth, the doors to Monkey World were flung open in the summer of 1987.

Many of the first inmates were chimpanzees rescued from photographers in Spain, who used them as tourist props.

Jim campaigned vigorously against the cruel trade, even lobbying Margaret Thatcher to crack down on the abuse as the campaign won national support. An Adopt A Chimp scheme was soon launched to help fund the rescues.

Monkey World soon became the fastest-growing tourist attraction the south.

In 1993, Jim met fellow American Alison, a primate specialist who went on to become his second wife.

The pair became stars in their own TV series - Monkey Business - screened in more than 230 countries.

Monkey World was awarded the Animal Welfare Award by the Universities Federation for Animal Welfare in 2003.

Jim also threw his weight behind numerous other anti-cruelty campaigns, including the use of monkeys in biomedical research and the trading of live primates.

In 2004, the plight of Naree, a chimp who was being cruelly treated at a Bangkok zoo, again earned national recognition and the attention of Prime Minister Tony Blair.

Monkey World now houses more than 160 apes of different species and welcomes half a million visitors a year. Jim received the MBE in 2006.

Mr Hermer said Jim demanded high standards of his staff but was "greatly admired" and respected by them. "Jim's desire was that Monkey World would live as his legacy for the future. That's absolutely what will happen," he added.

He said Monkey World would open as normal today and staff would continue Jim's work.

"They will grieve quietly on their own and come into work and carry on. There will be a fairly sombre mood about the place for some time."

Jim leaves a daughter, Eleanor, 20.

A memorial service was due to be held this morning at St Paul's Church in Yonkers, New York.