Thomas Silverfish is the President of the Alchemists' Guild. He first appears in Moving Pictures as a significantly more important character than his role in Guards! Guards!. He is one of the co-creators of octo-cellulose (the Discworld equivalent of cinefilm) and, coincidentally, of Moving Pictures which descends upon Holy Wood like a fever and briefly makes stars of many, including Victor Tugelbend and Theda Withel.
In Men at Arms, Silverfish is still experimenting with octo-cellulose, this time as a material for billiard balls -very volatile billiard balls. Following the events of Moving Pictures, Silverfish goes on to produce another, peculiar element. Far heavier than lead, is produced from lots of ore, and most certainly does not go bang- despite the thoughts of his assistant. This new element is likely a take off on Uranium.
Thomas Silverfish as a movie director is modelled entirely on movie mogul Samuel Goldwyn, whose real name was Samuel Gelbfisch, who went by the literal translation of Samuel Goldfish before changing his name a second time to Goldwyn - neither Silverfish or Goldfish being particularly impressive names for a movie tycoon.
Goldwyn was responsible for a whole sequence of malapropisms known collectively as Goldwynisms, some of which are so well known now as to have passed into the vernacular. Silverfish uses a number of these Goldwyn quips (in one form or another) throughout the book, such as "you'll never work in this town again", "include me out", and "a verbal contract isn't worth the paper it's printed on".