Composer and cellist. His father was apparently a cellist at Eichstätt and probably was his first music instructor. In 1754 Johann gained a position as second cellist in Germany's finest orchestra, that at Mannheim; there he studied further (probably counterpoint and harmony) with Johann Stamitz. He remained at Mannheim until his death at age twenty-six. Most of his published works appeared after his death, when his music experienced a vogue in Paris and elsewhere. He composed more than forty symphonies (six symphonies à 4 partiesop. 1); Masses; concertos; trio sonatas.
Fils' early death and the lack of information about his life gave rise to several legends: In a 19th Century dictionary one can read that he died from his bad habit of eating spiders, which he assured his shocked contemporaries, tasted just like strawberries!.