Papin

Theory 1
The apprentice of the Thaumaturge Corlian. He was an enthusiastic thaumaturge and was always grateful for being able to be under his master's tutelage. He agreed to sacrifice himself for one of Corlian's experiments and became undead. It was strangely mentioned by his master that "if he were to succeed [in the search for immortality], he would not have truly reaped the benefits of his apprenticeship". Which implies that Papin is most likely the undead left behind in one of the Conserver offices of the Archive when also taking into consideration that the undead was not wearing the strange helmet mentioned in the pieces of parchment.