Dr. Thomas served as director of one the most important repository of arms and armour in the world: the Waffensammlung, i.e. the Arms Collection of the Hapsburg Imperial Court, now a division of the Museum of Art History (Kunsthistorisches Museum) in Vienna. He studied art history, history, and languages. He began his career at the Waffensammlung in 1934; his principal aims—for the realization of which he has done research all over the world—have been the correlation of arms and armour history with generic art history, the development of refined methods of historical research, the installation at the Kunsthistorische Museum of effective and scientific restoration laboratories, and the reorganization and display of the entire Hapsburg collection in correct chronological order. He is the author of about two hundred publications in monograph and book form.