Emeritus Professor Issac (Ian) Kaplan passed away on November 11, 2021. Ian joined the UCLA faculty in 1965, following a PhD at USC (1961), postdoctoral work with Sam Epstein at Caltech (1961-62), and a visiting scholar position at Hebrew University (1962-65). At UCLA Ian started a world-leading stable isotope laboratory with a special emphasis on carbon and sulfur. With his many students and postdocs, Ian made early contributions that spawned entire fields of geochemical inquiry, including isotopic signatures of microbial processes, the influence of pore water chemistry on diagenesis, organic geochemistry of meteoritic materials, microbial sulfur cycling, gas hydrate geochemistry, and the organic geochemistry of Precambrian sediments. It is remarkable that many of these topics are now disciplines unto themselves, and that all can point to foundational papers by Ian. The scope of his contributions is encapsulated in the Geochemical Society’s Special Publication Volume 9: “Geochemical Investigations in Earth and Space Science: A Tribute to Issac R. Kaplan”. Ian’s pioneering research in organic geochemistry was recognized with the 1993 Treibs Medal of the Geochemical Society. He was also elected a Foreign Member of the Russian Academy of Natural Science (1998), and he received the American Association of Petroleum Geologists Division of Environmental Geology President's Award for career achievement in the field of environmental geology (2002). Ian founded the Global Geochemistry Corporation in 1975, which applied geochemical principles to molecular characterization, age dating, and kinetics of diagenetic transformations of organic compounds – essentially a commercial application of what he termed "forensic environmental geochemistry”. Ian transitioned to Emeritus status in 1993, but continued to be active in the department for many years. He is missed for his insightful, innovative perspectives and warm collegiality.