George Gilchrist started out in behavioral ecology of butterflies, but soon switched to thermal biology and evolution. We began working together on Drosophila projects while he was a grad student with Joel Kingsolver. We soon undertook a series of shared studies of acclimation and cross-generation effects, and did a large experiment in laboratory natural selection on knock-down temperature. Later we moved to the field to study rapid evolution of geographic clines, and shared a memorable Drosophila-collecting trip to Chile with two Catalonian colleagues. George was the ideal collaborator. He always brought total energy and enthusiasm even to the most tedious experiments. His statistical, analytical, and graphical expertise was legendary. He was always there to share his understanding of ecology, evolution, and physiology. On a personal level, George was self-confident and took delight in defending his opinions, but he would change his views when convinced by data. He took teaching and mentorship seriously. We co-taught a course in Animal Diversity. George made special efforts to engage and interact with students, but with results that surprised us both. George was a friend, a mentor, and leader in science, teaching, and the good life.