Willy Haeberli, the University of Wisconsin Raymond G. Herb Professor of Physics Emeritus, passed away on October 4, 2021, at the age of 96. Willy trained generations of students, post-docs, and international collaborators in the intricacies of planning and making nuclear-spin-physics measurements. His insight guided our development of polarized ion sources and polarized targets, and their subsequent use in new, increasingly precise measurements of very small nuclear-spin-dependent effects. I was fortunate to work with Willy in the 1960s. His large Wisconsin research group’s early successes were seeds that grew steadily over the next 50 years into his exceptionally rich nuclear polarization physics legacy.