Isaac

Isaac is a ghostly figure who, during the time of Ultima IV, haunts The Inn of the Spirits in Skara Brae.

Sloven tells the Stranger to seek out Isaac by staying at the inn until he appears and then to ask him of the white stone. Upon doing so Isaac will tell the Stranger that the white stone is atop the Serpent's Spine but it can only be reached by one who floats within the clouds.