Eyesnack, from Ultima Underworld
When meeting Eyesnack on the fifth level in Ultima Underworld I near Shanklick, the Avatar was surprised that he was a man of the arts, loving to play the flute. He offered to teach the hero a special melody, the Avatar only had to get a flute. After getting one, Eyesnack taught the melody and the hero promised to practise it.
The melody proved to be the key to make the Cup of Wonder appear on the third level.