Thanks, neither read nor seen silence of the lambs (so how do I recognise the character names? weird.) but will look it out and see how far I get.
G

Susie and Gauis

A Deuteragonist is

a person who serves as a foil to another

so can be either a side-kick or an antagonist.

Going back to Susie's line of thought...

I suppose I'd call him an antagonist because he is 'anti-good', while a pro-tagonist seems to be for-good? Or perhaps that we are 'for' a protagonist and 'anti' an antagonist?

I think what you mean are the hero and anti-hero popular in fiction. The main protagonist may be an anti-hero - Hannibal Lecter, or Raskolnikov (Crime & Punishment) - or they could be the hero - Sherlock Holmes.

In Crime and Punishment the detective, Porfiry Petrovich, seems to be the main antagonist, while the blakmailer and suspected wife-murderer, Svidrigailov, is a mirror of the MC. Both play a large part in the novel, so would this be an example of a worthy and powerful Deuteragonist and Tritagonist?

James