We are sad to report that Hans Rosling, a friend and teacher we both admired a great deal, died February 7. He was 68 years old.

Like many people, we first became aware of Hans when he gave a mind-blowing TED talk in 2006. He had spent decades working in public health, with a focus on poor countries, and he used his talk to share some surprising facts about how life is getting better, even for the world’s poorest.

We loved his message, but even more, we loved the way he delivered it. (We weren’t alone: That talk has been viewed more than 11 million times.) We had been trying without much luck to explain some of the same ideas, and Hans found a breakthrough way to make them clear and compelling. He could make you laugh and get you excited about the subject, while explaining something super-important. It was magical.

Later, we got to know Hans and his family personally, and we discovered that off-stage, Hans was pretty much the same person. Having dinner with him was every bit as fun and inspiring as watching him lecture.

In the last year of his life, Hans sent us a very touching letter. He told us that he had cancer, and then he made a request. He wasn’t asking for any personal favors. He simply hoped that we would promise to keep spreading the message he was so passionate about: that the world is making progress, and that policy decisions should be grounded in data. Of course we were happy to make that pledge. Hans was a great champion for the world’s poorest, and for clear thinking. He was also a wonderful man and we will miss him a lot.

If you want to know more about Hans and his work, we recommend this short article in Nature, any one of his many TED talks, and any of the many videos he posted on his Gapminder site.