Hans Wilhelm Eduard Schwerdtfeger (9 December 1902 – 26 June 1990) was a German-Canadian-Australian mathematician who worked in Galois theory, matrix theory, theory of groups and their geometries, and complex analysis.
"In 1962 he published Geometry of Complex Numbers : Circle Geometry, Möbius Transformations, Non-Euclidean Geometry which:
...
should be in every library, and every expert in classical function theory should be familiar with this material.
The author has performed a distinct service by making this material so conveniently accessible in a single book.
" - O'Connor, John J.; Robertson, Edmund F., "Hans Schwerdtfeger", MacTutor History of Mathematics archive, University of St Andrews.