Frei Otto (1925-2015) is an inspired choice for the Pritzker Prize. When I was a young architect, he was the man of the moment. I thought that his German pavilion at Montreal’s Expo ’67 was the best building of the exhibition. The sense of fluid, uncompartmented space created by the tent structure was something entirely new. That was just a warm-up for his breathtaking Olympic Stadium in Munich. I saw that building in 1972 and wrote about it—my second ever published article. Otto was later overshadowed by postmodernism, and by celebrity-driven architecture, but his lightweight architecture prepared the way for architects such as Piano, Foster, and Grimshaw. Otto—an engineer as well as an architect—never used structure as a fashion statement; his solutions were always rooted in iron-clad logic.