I didn’t know much about YouTube star John Green until a few months ago when my kids told me about his best-selling novel The Fault in Our Stars. It’s a deeply moving and, at times, surprisingly funny story about two teenagers with cancer who fall in love.

Later, I watched some of John’s video blogs and Crash Courses and was really impressed. People my age may not be John’s target audience, but I could quickly understand why millions of teens flock to his books and videos. One night I sat down to look at one of his online courses and then suddenly realized more than an hour had gone by as I watched John tackle complex ideas in history, biology and other subjects.

What impresses me most about John is his courage to ask tough questions—about cancer, the conflict in the Central African Republic, even how giraffes have sex—and then answer them in a way that is entertaining while at the same time super informative.

I asked John to come on part of my recent trip to Africa and found he was a terrific traveling companion. In Ethiopia, we visited health posts helping to vaccinate kids living in remote areas of the country; discussed the challenges of agriculture in Africa with a group of small farmers; and had an amazing conversation about growing up in Ethiopia with students at Addis Ababa University.

We also helped John conquer his fear of flying in a helicopter (though I’m not sure telling him how much safer it is than riding a motorcycle really convinced him).

As you can see in these videos, John’s endless curiosity was one of the highlights of our travels together. At every stop, he asked thoughtful questions about tackling poverty, getting young people involved in philanthropy, and tapping the power of storytelling to change the world.

So John, thanks for the great conversations and the company. I never thought of fighting poverty and disease as decreasing world suck and increasing awesome, but you convinced me that it’s as good a description as any other.