Steve Shirey is a pioneering geochemist whose career has greatly advanced our understanding of Earth's crust and mantle evolution through innovative use of geochemical tracers and radiogenic and stable isotopes. Shirey’s research, spanning processes from the Archean to today, combines field work, laboratory innovation, and theoretical models, significantly expanding our knowledge of key areas in Earth science. In studying Archean crust-mantle evolution and mantle heterogeneity, he identified and characterized a unique group of rocks called sanukitoids, providing essential insights into mantle melting processes in Earth's early history. By applying isotopic systems, especially the rhenium–osmium method, Shirey demonstrated that the Archean mantle was already chemically diverse and depleted in incompatible elements—a breakthrough that transformed models of early mantle evolution. His work on mantle xenoliths and eclogites set new standards for dating and interpreting mantle processes. Shirey’s research on cratonic lithosphere formation and stability, notably his studies of sulfide inclusions in diamonds, advanced our understanding of the age and structure of the lithospheric mantle beneath continents. By linking diamond geochemistry with seismic velocity data, he established a strong connection between diamond types and the physical structure of the mantle, providing evidence that the Wilson cycle–style plate tectonics began as early as about 3 billion years ago. Equally influential is Shirey’s work on sublithospheric, or “superdeep,” diamonds. He has been a leading figure in interpreting these rare samples as natural records of deep mantle processes, particularly those involving subduction and fluid recycling into the transition zone and lower mantle. His models connect diamond formation with deep-focus earthquakes and suggest that superdeep diamonds can reveal the periodic assembly and breakup of supercontinents, offering new insights into Earth’s interior dynamics. Beyond his scientific achievements, Shirey demonstrates AGU’s core values through mentorship, leadership, science advocacy, and ethical standards in science, with a dedication to diversity, inclusion, and scientific integrity. His has worked tirelessly to promote science policy in the United States. Shirey’s career has been marked by technical excellence, bold scientific vision, and dedication to the scientific community, and his contributions embody the spirit of the Hess Medal—illuminating Earth’s dynamic interior and its evolution through deep time. —Michael Walter, Earth and Planets Laboratory, Carnegie Science, Washington, D.C.