To ministers and heads of state, he was a sought-after adviser, pointing the way toward reforms that boosted farm yields, educational standards, and economic prosperity. To the scientific community, he was an unstinting champion of innovation and rigorous evidence. To his students, he was a passionate teacher and mentor. To thousands of his fans on social media, he was a fount of insight, optimism, and good humor. To us, he was a dear friend and extraordinary colleague.