Omori was one of the first prominent mixed martial arts competitors of his era. He helped to initiate the Vale Tudo trend of the 1920s and 1930s in Brazil. Geo had an extensive fight history engaging fighters of various styles including capoeira, boxing, and wrestling. A 1928 issue of The New York Times highlighted one of his fights against a "negro" capoeira fighter, in which Geo Omori won. He fought many members of the Gracie family including George Gracie and Carlos Gracie. His feud with Carlos Gracie is well documented.