Aria, from Ultima IX
The Avatar was first put on her trail when the female monk Kimberly told him of the theft of the Serpent. After arriving on Buccaneer's Den, it didn't take long to find the hideout, where Aria and Dunstan were arguing what to do next. They were surprised and killed by the Avatar in the following battle.
It was later revealed after freeing the Serpent, that the Guild of Buccaneer's Den was behind the crime.