Mr Cooper had failed to resurface after setting out for a dive at about 10.30am on Sunday morning.
Mr Nathan was described by a friend who wished not to be named as a "nice, caring guy". She said it had been a tough morning. "He was our mate ... he was our hero."
She said he had just gone to help with the search efforts but had not survived.
A Facebook tribute read: "Our dear nephew died in tragic circumstances while helping in a rescue. You were always helping others Roger and you will be greatly missed by the family in NZ and Australia. R.I.P darling."
He had been living at the beach.
Witnesses said Mr Nathan appeared to have let go of Mr Cooper's body before he climbed on to a rock to catch his breath, but was washed-off and disappeared.
A local said it appeared Mr Nathan had taken the weight belt off Mr Cooper before trying to bring him ashore.
Mr Cooper had had a leg amputated after a road crash in 1989, he was described as having extensive diving experience and had previously worked for Dive HQ.
It is understood he had been diving with two others when he got into trouble.
Police and the Lowe Corporation Rescue Helicopter joined the search for him soon after 3pm.
Waves crashed in the distance as Hawke's Bay Today spoke to locals yesterday, about 400 metres off the coast a New Zealand police dive boat was still at sea, searching for Mr Cooper's weight belt and bag.
A Pourerere resident who had given the five-person New Zealand police dive squad beds for the night said he had also comforted some of Mr Cooper's family during the search.
He said divers flocked to the area regularly for crayfish, kina, paua and mussels.
He said typical dive times were about half-an-hour to an hour, most were free divers but he understood Mr Cooper had gas tanks.
The area where the divers met their fate is about two to three metres deep with some big rocks.
Locals said Mr Nathan's father had just arrived back to news of his son's passing, having been away on a trip.
Retired Central Hawke's Bay Deputy Chief Fire Officer Owen Spotswood, who owns a bach at the beach, said it was one of the safest on the Hawke's Bay coast and during the summer divers arrived by the dozen.
Yesterday's mild weather had brought many to the beach for a mid-winter dive.
With no cellphone coverage in the remote area, search and rescue teams had needed to use residents' telephones during their mission.
Hastings store Dive East owner Chris O'Connor said he and his wife had known Mr Cooper for years.
He said his friend usually dove for kina and crayfish and stopped by the shop frequently.
"He would always give up the weather conditions, whether it was flat or murky."
"He had certainly done a lot of diving."
This tragedy, which has taken the drowning toll in Hawke's Bay this year to four, was the latest in a string of diving tragedies in the area, with many recorded dating back over a century.
