Experience Tumblr Like Never Before
Vis's surname at the start of TWOTM is Solus, meaning "one", "sole", "lonely". Presumably, this is a standard surname given to kids in orphanages.
Throughout the book are constant references to his identity issues: the constant lying, his relationship to his names and titles (Vis/Diago, the Telimus surname, the title of Catenicus), everything about the Suus beach episode, etc.
And in addition, the book ends with us seeing multiple versions of him across what seems to be different dimensions.
Here's the synopsis for the sequel, The Strength Of The Few:
Essentially, he goes from having a name that means "lone" to being more than one. I dig the irony (intentional or not.)