Before taking up music as a serious profession, Schumann wrote novels. Of his two attempts, Juniusabende was completed in 1826; Selene was not completed.
Chopin was a prolific letter-writer and also a keen caricaturist. The Museum of Caricature and Cartoon Art in Warsaw is organising a caricature competition in his memory, named "Chopin's Smile".
Mahler is considered an Austrian composer as he spoke German and was both a citizen of the Austro-Hungarian Monarchy and a pillar of the Viennese music establishment. Strictly speaking, however, he was Czech: he was born in the Czech village of Kaliště.
Schumann switched his ambitions from pianist to composer after permanently damaging his right hand. History doesn't relate exactly how, but it's thought that either Schumann was using a mechanical device to improve his ability to use his fingers independently, or that there was a failed attempt at surgery, with the same object in mind.
There is debate as to what was Chopin's birthday - the record says 22nd February, his family celebrated March 1st. His Scottish benefactress Jane Stirling claimed to be the only one to know the true date: she wrote it down, put the scrap of paper in a sealed box and placed it in Chopin's coffin.
Mahler was a terrible student at his grammar school, described by his teachers as "absent-minded, untidy and daydreaming".
While the legacy of Chopin, Schumann and Mahler is as composers, all three made a living from other things in their lifetimes: Mahler as a conductor, Schumann as a music critic and Chopin as a pianist (admittedly, mainly playing his own music).
Schumann’s name translates into English as Bob Cobbler, Mahler’s as Gus Painter. We couldn’t come up with anything for Chopin...
Our three composers span a range of different backgrounds. Mahler was the son of a country pedlar and carter: he received his first music lessons from the bass player in the municipal band. Schumann came from a solid bourgeois background: his father was a writer, publisher and bookseller. Chopin was brought up with the nobility: although his legal father was not noble, some Chopin experts think that he may have been the illegitimate son of an aristocrat.
Mahler is possibly the only composer who could have come up with idea of a funeral march to the tune of "Frère Jacques". It appears in his first symphony.
Chopin never wrote an opera. However, an opera was written about him (using arrangements of his music) by the Italian musician and critic Giacomo Orefice. It's being played in Warsaw in 2010 (http://www.bachtrack.com/find-an-opera/What/work=31114-Chopin).