Listener

The Listener is an imp which was summoned by the Guardian to serve as his spy in the underground complexes beneath Castle Britannia. It appears in Ultima Underworld II

Description
The Listener was a magical creature which secreted itself in a series of tunnels filled with magical flames near the waterways beneath Lord British's castle. From here it spied on the doings of the men above and reported its findings back to the Red Titan.

The sorceress Altara would reveal the existence of this being to the Avatar after the hero attempted to gain her confidence by mentioning Bishop. She would direct them to slay the imp with a magically prepared dagger and to return to her after the task was done. Once the Listener was slain, Altara would accept the Avatar as an ally in her private opposition to the Guardian, and would begin to assist the hero in their quest to free their people from the blackrock dome.