Cosme McMoon was the name of the character played by the actor Stephen Fry in the 2016 film "Florence Foster Jenkins." McMoon is depicted as Jenkins' devoted accompanist, and their relationship is a big part of the film. However, this was a fictionalized portrayal and there was no real-life Cosme McMoon.
Florence Foster Jenkins' real-life accompanist was Cosmé McMoon, who was actually a woman, although she was known for her androgynous appearance. She was a talented pianist who worked with Jenkins for many years.
If you are interested in learning more about Florence Foster Jenkins' real life, I recommend exploring sources like biographies and archival materials.