Otto von Bismarck | Otto | Georg Solti | Otto III | Otto Piene | Otto I, Holy Roman Emperor | Otto I | Georg Philipp Telemann | Otto Preminger | Johann Georg Wagler | Georg Wilhelm Friedrich Hegel | Otto II | Otto Dix | Georg Trakl | Georg Forster | Otto Natzler | Otto II, Holy Roman Emperor | Otto Binder | Georg Cantor | Georg Büchner | Georg Baselitz | Otto Skorzeny | Otto Schenk | Otto of Brunswick | Otto Kerner, Jr. | Hans-Georg Backhaus | Otto Steinbrinck | Otto Kerner | Otto IV, Holy Roman Emperor | Otto IV |
He also directly observed the work of Hippolyte Bernheim (1840–1919) in Nancy, Jean-Martin Charcot (1825–1893) at the Salpêtrière in Paris, Frederik Willem van Eeden (1860-1932) and Albert Willem van Renterghem (1846-1939) in Amsterdam, Ambroise-Auguste Liébeault (1923-1904) in Nancy and Otto Georg Wetterstrand (1845–1907) in Stockholm, at their respective clinics.