As I have mentioned more than once on this blog, I served my apprenticeship as a historian of science working for ten years in a major research project into the external history of formal or mathematical logic. During the semester, we held a weekly research seminar in which one or more of the members of the project would present a talk on the current state of their research. These seminars were held early evening and afterwards we would all go for a meal at a local Italian restaurant. I think, I probably learnt more through the discussions during those meals than through any other part of my life as a student.
From time to time those research seminars would be graced by a guest lecture by visiting historians. Over the years I got to hear lectures by many of the world’s leading historians of logic and mathematics. More important was being able to talk informally with these luminaries of the discipline during those post seminar meals.
One of those guest lecturers was Martin Davis, not only one of the best historians of twentieth century meta-logic but also a world class logician in his own right, who died 1 January. He held an excellent lecture on the American logician, Emil Post (1897–1954), who published a paper in 1936 giving an almost identical solution to the Entscheidungsproblem as Turing.
It was the meal after the lecture that we will forever remain in my memory. Martin was travelling through Europe with his wife and the two of them were incredibly friendly and delightful diner companions.
Two things are particularly present in my mind. The first is being in full flow in my inimitable style answering a question that Martin’s wife Virginia had posed about something in logic, when I suddenly realised that I, a mere student, albeit a mature one, was sitting between two of the world’s leading historians of logic, who were listening intently to what I was saying. Feeling somewhat more than flustered, I somehow managed to finish what I was saying. Nobody said anything negative.
The other was an incredible display of generosity from Martin. Amongst his publications, was a book that he edited called The Undecidable, a collection of the original papers on the topic from Post, Turing, Gödel et al. During the course of the meal, I asked Matin if there were plans to republish it as it was out of print, and I couldn’t get hold of a copy. He asked what I was doing after the meal and if I had time to accompany him back to his hotel. I said yes. When we got there, he gave me his personal copy of The Undecidable. I was mind blown.
Many years later I gave it to my professor, Christian Thiel, who has a very impressive collection of logic books. I was sad when I read of Martin’s death yesterday, remembering a very kind and friendly man, who once did a student a very generous favour.
The Renaissance Mathematicus 
I met Martin Davis when he gave a talk at the Rutgers’ colloquium series, on some consequences of the MRDP theorem, the solution to Hilbert’s 10th problem (then recently proved). MRDP stands for Matiyasevic-Robinson-Davis-Putnam. Martin Davis, Julia Robinson, and Hilary Putnam collaborated for years on the initial work. The final keystone was provided by Yuri Matiyasevic. Here’s what Davis said about this in his preface to Matiyasevic’s book Hilbert’s Tenth Problem
I always think of Davis as a logician, so it’s interesting to get a historian’s perspective.
Martin was a historian of twentieth-century meta-logic, which he went on the develop in his logical work
I simply meant that that’s how I think of Davis. However, did you mean that he started as a historian and later went on to logic? Or just that he did fundamental work in both fields? We certainly agree on that.
But I was curious, so I looked into his bio a bit. His thesis advisor was Alonzo Church; his thesis, “On the Theory of Recursive Unsolvability” (1950), was on the hyperarithmetic hierarchy and also on Hilbert’s 10th. All his publications from the 50s (as listed in JStor) were in logic. (Including lots of reviews by him.) His first book, Computability and Unsolvability, was from 1958; the historical collection The Undecidable from 1965.
He gave an interview in 2008 (Notices of the AMS 55:5 p.560-571). There he recounts getting interested in logic as an undergrad at City College, first from a reading course with Post. “By the time I graduated City College, I knew I wanted to be a logician.”
So it’s clear that he started his career as a logician; the historical work came later.
Incidentally, given all the nonsense written about Cantor and insanity, I was amused to read this passage in the interview:
Harold Davis here, Martin’s son. Martin’s professional career was as a logician, mathematician, and computer scientist, probably in that order. He was a man of wide-ranging intellectual interests. The history of Math was something like a retirement passion for him. You can find a good summary of his professional career at https://mathshistory.st-andrews.ac.uk/Biographies/Davis/
Thank you 🙃