Isaac

Isaac is a ghost who haunts The Inn of the Spirits in Skara Brae during Ultima IV.

Description
The old hermit of Cove, Sloven, could tell the Stranger to seek out the ghost of Isaac in the City of Spirituality in the course of the quest to find the white stone. After staying a night at Tyrone's hostelry, the hero would encounter the apparition, who would reveal the reason for his restlessness after death was rooted in his inability to complete the Quest of the Avatar.

Upon asking after the stone, Isaac would reveal to the Stranger that it lay in the mountains of the the Serpent's Spine and that it was inaccessible save by one who floats within the clouds.

Trivia

 * In the Nintendo remake of Ultima IV, Isaac freely gives the same information, without being prompted by other characters.
 * In the document discovered by historians Robert De Main and Carlotta Stein, which purports to be the Avatar's personal diary, the Stranger describes Isaac as seemingly being able to speak telepathically from within one's own mind, and remarks on how non-frightening Isaac was, despite being the first ghost ever encountered by the Avatar.