
Rainer K. Sachs
Rainer Kurt "Ray" Sachs was a German-American mathematical physicist, with interests in general relativistic cosmology and astrophysics, as well as a computational radiation biologist. He was professor emeritus of Mathematics and Physics at the University of California, Berkeley, and adjunct professor at Tufts Medical School.
Excerpt from Wikipedia, available under CC BY-SA 4.0.
Books

General Relativity for Mathematicians
1977
ISBN 9781461299035