In Feet of Clay, Mr. Joshua H. Catterail is the pompous and bigoted clothing factory owner who writes a series of small-minded letters to the Watch protesting at Dwarf and Troll officers patrolling in Park Lane, where he lives.
Samuel Vimes meets him in the flesh when Dorfl rips his factory apart in a bid to incite his golems to riot. Vimes is not impressed, noticing that Catterail sweats and bullies his workers, who to a man and woman have a Cockbill Street mentality. Even more annoying, he does not recognize Vimes, and pretends to be good friends with "your commander". He even presumes that the Watch are there for his use. "Now, what I want you to do is..." (emphasis added).
Told by Carrot that Catterail is the writer of the small-minded letters, Vimes' reaction is to recruit some zombies to patrol up on King's Down. Catterail can't complain about that, as they are completely human...
Henry Root had a similar turn of phrase, the creation of William Donaldson. Catterail is probably a play on the word 'catterwail'.