"The MacArthur Foundation chose Witten in 1982 for one of its earliest “genius” grants, and he is probably the only person that virtually everyone in the theoretical physics community would agree deserves the genius label. He has received a wide array of honors, including the most prestigious award in mathematics, the Fields Medal, in 1990. The strange situation of the most talented person in theoretical physics having received the mathematics equivalent of a Nobel Prize, but no actual Nobel Prize in physics, indicates both how unusual a figure Witten is, and also how unusual the relationship between mathematics and physics has become in recent years. When I was a graduate student at Princeton, one day I was leaving the library perhaps thirty feet or so behind Witten. The library was underneath a large plaza separating the mathematics and physics buildings, and he went up the stairs to the plaza ahead of me, disappearing from view. When I reached the plaza he was nowhere to be seen, and it is quite a bit more than thirty feet to the nearest building entrance. While presumably he was just moving a lot faster than I was, it crossed my mind at the time that a consistent explanation for everything was that Witten was an extraterrestrial being from a superior race who, since he thought no one was watching, had teleported back to his office. More seriously, Witten’s accomplishments are very much a product of the combination of a huge talent and a lot of hard work. His papers are uniformly models of clarity and of deep thinking about a problem, of a sort that very few people can match. Anyone who has taken the time to try to understand even a fraction of his work finds it a humbling experience to see just how much he has been able to achieve. He is also a refreshing change from some of the earlier generations of famous particle theorists, who could be very entertaining, but at the same time were often rather insecure and not known always to treat others well."