Specialist in ancient Greek and Roman art, particularly vase painting. Diepolder was first a student and collaborator with Ernst Buschor in Munich. He was the Assistant (1925-1937) and then Director (1937-19??) of the antiquities collection at the Munich Museum. In 1936 he authored the volume on the Penthesilea painter for Bilder griechischer Vasen series edited by J. D. Beazley and Paul Jacobsthal. Named Honorary Professor at Munich University in 1946.