Here is the character description at eNotes.  You can find out more about this character and others by visiting the link below,

Adso of Melk is an elderly Benedictine monk who writes of his experiences as a young novitiate who accompanies William of Baskervilles on his trip to a northern Italian abbey in 1327 where they encounter a series of murders. Adso thus plays two roles in the novel: in the first place, his is an older voice, one that has had time to consider and reflect on the events of which he writes. In the second, he is young, innocent and naïve, the younger son of a wealthy nobleman, pledged to the church. The Name of the Rose is very much the story of Adso’s coming of age; he loses his virginity to a young peasant girl, and he grows from ignorance to knowledge. He encounters the most pressing theological debates of his day at the abbey, as well as a thirst for knowledge that leads several other young monks to their deaths. He also plays “Watson” to William’s “Sherlock” in the investigation of the murders.