Leon Fischer is a New York-based attorney specializing in art law and commercial litigation, best known as a lead claimant in high-profile Nazi-looted art restitution cases. He is the grandson of Fritz Grunbaum (1880-1941), the Viennese cabaret artist and art collector whose collection of over 400 works—primarily drawings and watercolors by Egon Schiele, along with pieces by Klimt, Kolo Moser, and others—was looted by Nazi authorities after Fritz and his wife Lilly were arrested and murdered in the Dachau concentration camp in 1941. With no direct children, Grunbaum's heirs, including Fischer and his brother Matthias Fischer (both New York residents) and nephew Timothy Reif (a former U.S. State Department official), have pursued claims asserting rightful ownership based on Grunbaum's documented collection and Nazi seizure records. Fischer has been instrumental in several landmark restitutions, including a 2019 settlement with the Museum of Modern Art (MoMA) for the return of Schiele's 'Portrait of a Man' (settled for undisclosed terms after lawsuit filed in 2018); a similar agreement with the Carnegie Museum of Art for 'Sunday'; and claims against the Art Institute of Chicago ('Girl in a Black Dress'), Santa Barbara Museum of Art, and private collector Nancy Wiener. These efforts, often filed in U.S. courts under the Holocaust Expropriated Recovery Act, have spotlighted provenance issues in museum holdings and resulted in deaccessions or shared custody arrangements. Fischer's cases underscore ongoing challenges in Holocaust-era art recovery, with critics noting rigorous provenance defenses by institutions. Beyond restitution, Fischer maintains a private legal practice in New York City.