RICHARD Harris — an Aussie doctor with 30 years of cave-diving experience who put his life on the line to save the trapped Thai schoolboys — is no stranger to tragedy.

The Adelaide anaesthetist and underwater cave explorer made the treacherous journey into the chamber where the boys have been trapped underground for more than two weeks on Saturday as part of an incredible international mission to save them.

He scuba dived 4km through cold, dark and narrow passages to reach the boys and assessed them as medically fit to attempt the risky escape mission, which is still ongoing.

British divers specifically requested the talented medic for the rescue operation which has already claimed a life of one of the cave divers taking part.

However, it is not the first time Dr Harris has found himself at the centre of a tragic rescue operation.

The well-known diver was also summoned for an extremely difficult and life-threatening cave diving mission in 2011, when he was tasked with recovering the body of his mate Agnes Milowka.

She ran out of air during an expedition at Tank Cave near Mount Gambier in South Australia, but Dr Harris had to find the strength to pull his mask on and recovered her lifeless body from the dangerous cave.

South Australian police specifically requested Dr Harris because of the complexities of the almost eight-kilometre stretch of winding underwater passages inside the perilous cave network.

Ms Milowka was a highly respected cave diver who had worked as a stunt diver on James Cameron’s 3D diving film Sanctum.

She is understood to have become disoriented during the tragic 2011 mission in South Australia and ran out of air while trying to work out how to navigate a difficult section of the cave.

The heartbreaking mission is just one of many over Dr Harris’ illustrious career, which have propelled him to become one of the most sought-after professionals in the field.

He’s been described as “essential” to the rescue bid to save the trapped Thai schoolboys because of his unique skills and experience.

“He’s an interesting character,” MedSTAR clinical director Andrew Pearce told reporters on Monday as the rescue efforts in Thailand continued.

“Harry is selfless, he is extremely thoughtful. He’s a quiet person. He is the type of guy who will give of his all.

“He was actually meant to be on holiday and gave up his holiday so that he could be part of this.”

Dr Pearce said Dr Harris was known globally both for his work as a doctor and his ability to retrieve people from difficult places.

“He’s using those skills at the moment, not only as a doctor but the added benefit that he happens to have this amazing ability to do what no-one else does in diving into very dark, tight spaces with not a lot of equipment,” he said.

“In this small fraternity of people, when you get asked for by name you’re known worldwide for your skills.”

Dr Harris was also the leader of record-breaking missions to explore a dangerous underwater cave system on New Zealand’s South Island.

In 2011 and 2012, he led a team of Aussie divers to record depths of 194 and 221 metres in what’s believed to be one of the world’s deepest cold water caves, searching for the source of the Pearse River.

He filmed the dangerous and complex mission for National Geographic.

It required the team to set up a series of survival pods at intervals to allow divers to decompress, rest and eat in the near-freezing waters along the length of an underwater river — an experience that could prove invaluable in the current rescue mission.

Foreign Affairs Minister Julie Bishop said Dr Harris had been essential to assessing the health of the trapped boys.

“He is an experienced diver, which is a great benefit because he’s brought all that expertise to assist the Thai government in this rescue mission,” she said.

Dr Harris entered the mountain in northern Thailand where the 12 Thai schoolboys and their coach were trapped on Saturday.

Overnight, four more boys were saved from the dangerous network as part of a rapid-fire operation, bringing the total rescued to eight.

That leaves four young soccer players and their 25-year-old coach still trapped.

— with wires