I've cheered his work in several columns, one of which was quoted in a blurb on the jacket of his second book, Stones into Schools. I've also watched huge American audiences devour his rambling, passionate lectures on the need for more girls' schools in poor countries.
This plea has garnered tens of millions of dollars for his institute, including $1.7 million collected by schoolkids in 2009 for Pennies for Peace (P4P), a program to buy school supplies for Afghan and Pakistani children.
So it was disturbing to watch a 60 Minutes exposé last week - and to read an online booklet by author Jon Krakauer, once a Mortenson fan - that accused Greg of lying in his books and of financial misfeasance. Among the allegations: that the Korphe story was untrue; that many of the 141 schools he supposedly built do not exist or are no longer functioning; and that his charity spends more on promoting his book and his lectures than on building schools.
In a written response to 60 Minutes, Greg says he stands by the facts in his books. His assistant Jeff McMillan told me by phone Thursday that Greg will publicly address all issues, and document all of his schools, once he recovers from a surgical procedure next week to repair heart damage. McMillan says the issue of accounting transparency will also be addressed.
I certainly hope so, because the Greg Mortenson phenomenon has become much larger than this larger-than-life man.
In an era where so much news is bad news, something about his upbeat story has touched a popular nerve. Three Cups of Tea offers a concrete prescription for how individuals can help in countries beset by Islamic radicalism. It puts forward the promise that education can change the mind-set that produced 9/11.
This is so, even though Greg's schools, no matter their number, can't make an absolute difference. Still, they symbolize the desperate need for educational facilities to replace the madrassas that train boys to become jihadis.
True, Greg has focused on girls' schools. This is exciting because many Afghan girls are willing to take huge risks to gain an education, a desire that was thwarted under the Taliban. However, in villages where there were no boys' schools, Greg has built facilities for boys, too.
Even Krakauer, who became a sharp critic, admitted on 60 Minutes that Greg "has done a lot of good. He has helped thousands of schoolkids in Pakistan and Afghanistan. He has become perhaps the world's most effective spokesperson for girls' education in developing countries. And he deserves credit for that."
What's also important about the Mortenson phenomenon is that Greg's approach is the correct one for any aid project in the third world. He insists on sitting down with locals, listening to their needs, and getting them to participate in building the project. This means the community has a vested interest in the outcome.
That is the way his staff rebuilt the girls' high school that I visited in Muzaffarabad, Kashmir; it had been destroyed in a 2005 earthquake in which more than 100 students perished. The surviving girls had studied in tents for two years, despite promises from Pakistan's government and other charities to begin construction. But with local labor, Greg's staff completed the job in a couple of months.
The Three Cups of Tea model - getting critical input from the grass roots - is the model other successful U.S. and private aid programs have followed. Failure to get local buy-in has doomed far too many foreign aid projects.
Indeed, the need to win local buy-in is essential to the entire U.S. strategy in Afghanistan. Greg did not originate this approach, but his book has come to symbolize it. This is one reason why the chairman of the Joint Chiefs, Adm. Mike Mullen, attended the opening of one of Greg's schools. It's also why Greg's book was made required reading for U.S. servicemen bound for Afghanistan.
So it would be tragic if Mortenson's errors - of omission or commission - tarnish the good he has done and the aid model he promoted. When I traveled with him, he hardly looked like a big spender; he dressed in a Pakistani shalwar khameez (loose pants and a long tunic), stayed in cheap guest houses, and drove in ordinary cars.
But he is famously disorganized, driving boards of directors to distraction, as his co-author described in Three Cups of Tea. I almost didn't get to travel with him because he failed to return phone calls.
It is easy to imagine that the Three Cups of Tea phenomenon grew too big for a visionary who didn't want to let go of control of his project. Yet a charity that collected $20 million in 2010 must meet basic standards of transparency and law.
It is also easy to imagine that Greg, who delighted in traipsing to the wilds of Pakistan and Afghanistan, was unable to create the bureacracy needed to match the explosion of funds pouring into CAI.
Whatever the real story, Greg owes it to those who believed in him to give an explanation. Otherwise, the 60 Minutes exposé will sap the idealism his work has inspired among so many Americans - including children.
I'm thinking of a close friend's 11-year-old daughter, who said that, when she grows up, she wants to be "like Greg Mortenson, only in Africa." Her school is collecting money for P4P, and classes compete to see who can raise the most money. Her mom says she is "heartbroken" by the stories about misuse of the funds.
I've told her that the principles that Greg promoted, and the schools he built, still stand, no matter any mistakes he committed. And I mean that. But I still hope he will set the record straight.
E-mail Trudy Rubin at email@example.com.