De Boer's position as executive secretary of the U.N. Framework Convention on Climate Change requires him to use three passports, two of which are constantly in cycle as he gets new visas. Three-quarters of the year, de Boer is on the road.
At past climate conferences, de Boer was often seen slipping out of the climate talks to indulge in hand-rolled cigarettes. While he quit smoking this year, de Boer is still known for his taste for beer, lobsters and the occasional party.
"He's a man who likes to live and has a great spirit of life," said the World Resources Institute's Morgan. "You can see him on the dance floor at the NGO parties in his Bali shirt."
'He walks the line'
De Boer often finds himself in the middle of diplomatic brawls, in part because that is how he has defined his job.
"At the end of the day, I'm not a player, I'm in a support role," he said. "But I do think that you can kick people in the backside and say you need to get serious about defining this long-term response. I think that needs to happen. The flip side is if I do it as a U.N. official, that can have implications for a secretary-general: Why is this idiot acting beyond the traditional role?"
To be sure, de Boer has irritated many.
"He's sometimes bullying," said a climate diplomat close to the 2008 Poland negotiations.
"My gut sense is he sometimes oversteps the role," added Elliot Diringer, vice president for international strategies at the Pew Center on Global Climate Change. "I think there's a case to be made that these times call for a more aggressive role for the executive secretary. But there are bounds to it.
"He walks the line," Diringer said. "And sometimes crosses the line."
Many sources who track U.N. negotiations say de Boer's blunt style helps keep the process honest.
"He's very outspoken," said Karsten Sach, a top environmental official for Germany. "I think we need to be outspoken in order to get the support from the public that we need to get."
"He can be very, very straight with people," explained Connie Hedegaard, Denmark's minister for climate and energy. "Personally, I like people who are very direct. And sometimes, in these intense negotiations, it's better that people are clear and straight then not really coming out with what they're thinking."
Environmentalists welcome de Boer because they see him pushing laggards forward on climate change.
"It's a hard job to make everyone happy," World Resources Institute's Morgan said. "And if the executive secretary of the UNFCCC makes everybody happy, then we don't make progress."
Mohamed El-Ashry, former chairman of the Global Environment Fund, said de Boer has had to make some adjustments in going from being a Dutch negotiator to being someone who is responsible to many more bosses.
"Yvo learned quite a bit on the job, because he came representing one government," El-Ashry said. "He can provide proposals, but he cannot corral them to go with one proposal."
That job, El-Ashry noted, belongs to the president of the annual climate conference -- a rotating gig that this December falls to Denmark's Hedegaard.
De Boer acknowledged that he has brought a little bit of his previous job into the current role.
"I've been a player, and now I'm the servant," de Boer said. "It takes some practice to be a good servant -- to shut up. But at the same time, I think a good servant doesn't always shut up. A good servant can say, 'Do you really want to eat this again? Shouldn't you be having more vitamins in your diet?'"