Reef, from Ultima Underworld II
Reef is the ghost of a dead officer of the kingdom's army in the Tomb of Praecor Loth on Rhiannon.
Reef stood directly beside Praecor Loth when the arrow from Lord Thibris killed his king. The whole thing drove Reef to madness. A madness that continued even after his death. His spirit constantly haunted through the corridors of the tomb and he became worse with each year.
In Ultima Underworld II, Reef didn't even listen to the Avatar, having totally drowned in his madness, babbling the whole time about Loth's death. He then totally snapped and attacked the Avatar, who destroyed him, his essence lost for all time.