Joe

Joe is a drunken fighter who, during the time of Ultima IV, lived in Britain and can be found drinking in the Jolly Spirits with his friend Joe.

Upon providing Joe with some rum he informs the Stranger that Joe can help him/her with the stones and upon further inquiry will tells the Stranger that the yellow stone resides in Despise.

Trivia
There is a bug in the Apple II and C64 versions of Ultima IV (and probably the other 6502 ports as well), which makes the conversation with Joe unavailable.