Kap was enormously influential in many fields of mathematics, through his papers, through his books, and perhaps most of all through his Ph.D. students and the many many additional students who, like myself, listened raptly to his courses. I remember well his highly entertaining and beautifully polished lectures from my student days in Chicago — whatever he taught, I signed up for the course, it being such a pleasure to listen to him. From being on the first winning team of the Putnam competition to being president of the AMS and National Academy member, his career was truly remarkable — you can find more information starting from the AMS website, http://www.ams.org/ams/48-kaplansky.html.
As the second director of MSRI, Kap served the Institute directly from 1984 through 1992. He greatly developed the reputation and influence of MSRI, building on the start provided by the founders, Chern, , and Singer. My own first experiences at MSRI were under Kaplansky’s directorship. As with everything he did, he paid attention to every detail of the operation — he boasted to me once that he personally read and signed every single letter of invitation that the Institute sent out during his eight years in office. He and his wife, Chellie, were also very present and available to the members — literally thousands will remember Kap’s musical performances at the Christmas parties. Among the many marks Kap left on MSRI was the start of fundraising activity. For example Kap formed the “International Board of Friends of MSRI”, and the connections made through this group are still of the utmost importance to us. Kap’s first paper appeared in 1939. After stepping down as MSRI director, at seventy-five, Kap went back to full time research mathematics, and returned to number theory, one of his first loves. Some of his most recent work, on integral quadratic forms, was published in 2003, when he was eighty-six.
Mathematically, Kap was my brother: he, the first student of Mac Lane, I, nearly the last. But he was much more an uncle to me who had been down most of the avenues that I later began to explore. He was always generous in advice, counsel, and in giving credit. I saw him nearly every day in my student days at Chicago, and again, nearly every day, over the first eight years I was MSRI director. Interacting with Kap was always a pleasure, crisp, clear, and somehow uplifting. It is one that I shall deeply miss.