A Cook Island Maori on his mother's side, Scottish-Irish on his father's (a ship's stowaway), he may be the new boy in town but he's closely linked to local iwi.
His wife Tracey (nee Rapana) is pure Ngati Pikiao. It was Tracey who convinced him to apply for the courts job, advertised when they were living in "Paradise", Dan's definition of the Cook Islands.
He'd taken his family there in 2007 supposedly to semi-retire, but when Tracey spotted an ad online for the Rotorua-based job, the timing was perfect.
Two of their children were of an age where they needed a more rounded education than "Paradise" could provide; cue the O'Briens' April arrival in Rotorua.
Disregard the "supposedly to semi-retire" in the preceding paragraph. Having recently stepped down from Fisher & Paykel Finance as manager NZ business operations, his arrival in "Paradise" was seen by locals as heaven-sent.
Within days he was "coerced" into sorting out financial problems plaguing one of the Islands' largest private companies, Pacific Distribution Ltd (PDL).
With PDL sussed, he became general manager of the Cook Island Trading Company's food group. A spell as a bounty hunter followed. Mynahs had invaded Aitu, threatening the island's bird sanctuary status. The Cook Islands National Heritage Trust wanted them gone. Ace marksman Dan joined the exterminators.
He'd have happily remained had not former Prime Minister Sir Geoffrey Henry shoulder-tapped him to become the Cook Islands National Olympic Committee's treasurer.
"I went in thinking I'd be doing 2-4 hours a week only to find the organisation insolvent, which put the Cooks in peril of losing its international Olympic status."
For the next 18 months, the financial fix-it man worked around the clock.
"In the Islands, sport is as big as religion. To lose IOC funding would have been tragic." His brief included a trip to Lausanne to prove (successfully) to the IOC the Cooks' funds had been redirected, not misappropriated.
Less than a year on he was mixing with the organisation's high flyers in Moscow - "a very interesting experience being with the Crown Prince of Dubai, prime ministers and presidents from different nations; they were surprised what a country of only 14,000 people could achieve."
A spin-off was a Kremlin dinner invitation. "President Putin and his predecessor [now prime minister] Dmitry Medvedev were our hosts, we were taken to parts of the Kremlin not normally open to the public. It was phenomenal, unbelievable in the terms of grandeur."
In Moscow, guns again featured. "We were allocated bodyguards, you could see firearms bulging under their jackets."
But that was small arms stuff compared with his visit to Uganda last September for a Commonwealth Games Federation meeting. By then he'd become the committee's chief executive.
Even for a man who's served in unnamed political hot spots Uganda was scary stuff. "The guards were carrying AK47s, it was certainly a bit unnerving. They were coming up and pressurising us for money supposedly for their sick kids. Uganda wanted to host the Games but we didn't feel it was the right place."
With the Cook Island's National Olympics committee finances sorted he again planned to taste retirement; others had different ideas. The Government was looking for an economic development commissioner; Dan was contracted.
"It was time for the Cooks to look for a hand up, not a hand out ... to become self-sufficient."
His job was tackling projects previously consigned to the "too hard" basket, concentrating on the one labelled "China". There is, he says, no such thing as free money from China.
Attention turned to the US to redress damage caused to lagoons by America's 1950s off-shore missile launches. "It was pay-back time, we put them on notice to rectify this."
Dan's Cook Islands swansong was last December's Pacific Leaders' Forum, his involvement in the areas of climate change and renewable energy.
Rotorua has not severed his Cook Islands links, a tightly braided plait hangs low on his back and he wears earrings - "symbols of my culture, recognition of my mother's Ariki [chiefly] lineage."
DAN O'BRIEN
Interests: Family, boxing (was a youthful bare knuckled pit fighter), hunting, fishing, darts, music (drummer in Cook Island cultural group performing in Spain), panning for gold, "I've got the fever", "dabbles" in golf.
On Rotorua: "Beautiful, but the smell can be overpowering."
Personal philosophy: "Age is what you put on your headstone to show whether you had a good innings."