By following the links I was able to construct the following list of Jack’s mathematical ancestors:
Jacob T. Schwartz, Ph.D. Yale University 1952
Nelson Dunford, Ph.D. Brown University 1936
Jacob David Tamarkin, Ph.D. St. Petersburg State University 1917
Pafnuty Lvovich Chebyshev, Ph.D. St. Petersburg State University 1849
Andrei Andreyevich Markov, Ph.D. St. Petersburg State University 1884
Nikolai Dmitrievich Brashman, Ph.D. Moscow State University 1834
Joseph Johann von Littrow, Advisor Unknown.
I recognized the names Chebyshev and Markov as soon as I soon them.
George Forsythe and Dunford were mathematical sons of Tamarkin, so George was Jack’s mathematical uncle. George was the first chairman of the computer science department at Stanford, as was Jack the first chairman of computer science at CIMS. 
I know I studied some of Forsythe’s work and I have a vague memory that he may have spent some time on the Caltech campus.
I was quite moved as I put this list together, especially when I saw so many of Jack’s
1. Forsythe’s entry is very brief. I also try to omit needless words, but the authors enforced too low a bound on the size of his entry.