The renowned cryptozoologist is known all over the country for his studies into the yowies, sea serpents and big cats that are said to have once roamed the Australian landscape. Some say they still do.

Mr Gilroy, who died over the Easter break, not only took people's sightings of strange creatures seriously, he viewed them scientifically, regularly travelling to the areas in question to investigate.

This included many visits to the South Coast area of New South Wales to look into sightings of Kangaroo Valley's legendary black panther.

The quest to find the valley's own big cat was led by the late Doris Blinman, a great Kangaroo Valley character who was nicknamed 'the panther lady'.

There were many theories over the years about the valley panther's origins; including that they were circus escapees or descendants of mascots released by overseas military personnel serving in the area after World War II.

Mrs Blinman's convincing reports of black panther sightings on her property in the 1980s and 90s even made international news.

"I've been six foot away from them, looking through the kitchen door," she told ACM's The South Coast Register at the time.

She said she saw two different panthers around her house and could tell them apart because one had a thicker tail.

"The cats came both at night and in daylight and delighted in eating the fruit from my grapevine as well as eating local wildlife, including a fruit bat," she said.

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While many scientists argue that Big Cat sightings are most likely feral cats, Rex Gilroy had no doubt they were the real thing.

Another local sighting was well documented in 2016, by Shane Gowan.

He and his cousins were driving the Captains Flat Road, towards Braidwood in the midst of the Tallaganda State Forest, when about a 100 metres ahead of them, they reported seeing an enormous cat crossing the road.

"It was huge, I've never seen a feral cat that big. It would have been 3-4 times bigger than the biggest cat I've ever seen," Shane told ACM's The Braidwood Times.

Shane said it looked like it weighed around 35 kilograms.

They stopped to take a photo, before gradually pulling closer. They inched forward, but after 10 metres, the cat darted into the bush.

Rex Gilroy's expeditions to Kangaroo Valley and Morton National Park were not only on the look out for traces of the black panther.

Over the decades he amassed thousands of reports of yowie sightings, dating from 1788 to the present day, and went on to establish the Hominid Research Centre.

During one trip to Shoalhaven in 2012 he told The South Coast Register about some local yowie reports.

"We have some very good leads from the localities we will be investigating, including recent sightings, claims and apparent freshly-abandoned campsites where stone tools have been found in the Morton National Park," Mr Gilroy said.

"Hopefully this time we will obtain good physical evidence proving these primitive hominids exist," he said.

On that occasion Mr Gilroy was on the lookout for the "Nerriga Giant", after hikers reported finding huge footprints near a Shoalhaven River location, similar to fossilised footprints found in the Blue Mountains and Budawang Range.

Also on his radar for that visit in 2012 was a 1.5 metre tall hairy female hominid and small child that were claimed to have been seen by campers in Wandandian mountain wilderness.

On a pre-expedition visit to the area, Rex said he and his wife Heather found recently made crude stone tools.

Tim the Yowie Man, who writes a popular column for The Canberra Times, has paid tribute to Rex Gilroy.

"Rex leaves a last legacy of an unprecedented contribution to the Australian cryptozoological world, not just 'yowies' but more broadly including thylacines, sea serpents, big cats and much more," Tim said.

"A lifetime of research, passion and dedication to the cause. Rex, I dip my hat to you."