Rupert Bleakley

Rupert Bleakley is a vampire. Presumably part of the Ankh-Morpork League of Temperance, he works in what would, on Roundworld, be a most unusual place.

At a time when Sam Vimes is more than usually annoyed, he tells Fred Colon that he'd even swear in a 'damn gorgon'. Fred's reply is cut off very quickly: 'There's always Mr Bleakley, sir, he's getting fed up with working in the kosher butcher's and—'

'But no vampires. Never any vampires. Now let's get a move on, Fred.'

Presumably he sucks the animals dry quicker than gravity could expel the blood for them.

And of course, by the time of Unseen Academicals, the incidental detail reveals that a "damn gorgon" really is working for the Watch - alongside its first vampire...