Zoons

A race of people who, like the N'Tuitif of Howondaland, are pathologically incapable of lying. This is a drawback in a trading race, so the Zoons elect a Tribal Liar to do the negotiating for them. Other people get offended by this and think they should have picked a more acceptable term, like "diplomat" or "politician". The Zoons reply that this is exactly the point.

The Zoons run cargo barges between Ankh-Morpork and the hinterland. They'll also carry passengers, but presumably charge high prices, and, ironically, not many people trust them.

Esk runs into them in the form of Amschat B'hal Zoon, who was the current Liar at the time of Equal Rites.