#### by Carlos E. Kenig

I was one of Alberto Calderón’s graduate students at the University of Chicago from 1975 to 1978. This was a period of intense mathematical activity. During the 1976 Christmas break Calderón obtained his remarkable result on the boundedness of the Cauchy integral for Lipschitz curves with small constant. (The general case was obtained by Coifman–McIntosh–Meyer in 1981.) As soon as classes started in the winter quarter, I went to see Calderón in his office, where he was explaining his proof to Bill Beckner. There was real excitement in the air, which even I, a mere graduate student, could feel. Soon after, the annual meeting of the AMS took place in St. Louis in the midst of a terrifying cold spell and a terrible winter storm. In connection with the AMS meeting there was a conference in harmonic analysis at Washington University, the very first conference I attended. At this conference Calderón explained his proof with his usual elegance. One could also sense his pleasure in having finally made a dent in this problem, which he had thought about for so long. This work opened up entire new vistas of research, which are still being explored.

Shortly after our return from St. Louis, I asked Calderón for a thesis problem. His response was this: Find a problem yourself, and let’s discuss it afterwards. Fortunately for me, the recent work on the Cauchy integral had opened up many new possibilities. I chose to explore the theory of Hardy spaces on Lipschitz domains and went on to obtain my degree in 1978. Calderón was a mathematician of deep and original insights and also of great generosity with both his ideas and his time. I count myself as extremely fortunate to have been his student, especially at such a highly significant moment — an experience that greatly influenced much of my ensuing research.