In most other RPGs they're called NPCs. In WHQ Roleplay flavor they're called "Character Encounters". Page 153 of the Roleplay Book begins a useful section on how to introduce NPCs into the game, and gives some imaginative examples of Character Encounters.
In our next session, should things move in a certain direction, I have the following Character Encounter ready for the players ...
Von Keingelt is a mid-level noble whose holdings border the outskirts of Altdorf. His ancestors have the dubious honor of having been principal patrons of the sewer projects in Altdorf. His great-grandfather, Willhelm Keingelt actually produced the "design" of the twisting maze of sewer tunnels under the city - a design that was grudgingly adopted by the College of Engineers.
Because of this history, Lieder Von Keingelt is forever associated with the sewers. Whenever there is a problem in the sewers (and this happens with surprising frequency) the City leaders invariably pressure him to find a solution. Due to this constant stress, the Baron is a nervous wreck, and is also in financial ruins.
If the Warriors have been commissioned by Baron Leider Von Keingelt, roll below when they complete their mission:
1. The Baron discounts any evidence that the Warriors produce, refusing to pay and claiming that the job was never completed!
2-3. The Baron tells the Warriors that his funds are tied up in some civil works projects at the moment, but that he is expecting a payout "any day now". The Warriors can wait in the Settlement hoping to get paid. At the end of each day, roll 1D6. On a 6, the Baron's funding has indeed arrived and he pays the Warriors as promised.
4. The Baron hems and haws about how the Warriors fixed the symptoms but not the root cause of whatever problem they were sent to alleviate. He finally, after much argument, agrees to pay them 30-70% of the originally promised sum.
5. The Baron seems unusually distracted, but he pays the Warriors promptly the agreed upon amount.
6. The Warriors have done such an impressive job that Von Keingelt was awarded a reward by Karl Franz himself, and passes along to the Warriors twice the agreed upon payment!