Three characters in Robertson Davies' Fifth Business undergo name changes: Boy (Percy Boyd Staunton), Magnus Eisengrim (Paul Dempster), and Ramsay himself (Dunstable Ramsay)all undergo major chnages in their lives. These changes represent internal changes in each of the characters, and the name change illuminates the internal change in an external way. For each of the characters, a new life is begun. In order for this new life to be whole, the men need new identities as well.
For example, Ramsay's name is changed by a nurse, Diana. It is her job to take care of him after he has had a massive leg injury (due to the war). After being refused by Ramsay, Diana changes his name to Dunstan. It is also important given he has been declared deceased.
Boy Staunton needed a new start after a bad one in the Army. The name Percy only brought him painful memories. In order to begin again, Boy dropped the name Boyd.
Magnus Eisengrim began life as Paul Dempster. In order to fulfill his desire to be a magician, and given that Paul was not really the type of name a magician would use, Paul changed his name to Magnus.