Galileo Galilei, and yet people still refer to him by his firstname alone. It's painful to read.
It is, as if we refer to Isaac and Albert when speaking about Gravity and Relativity.
https://en.wikipedia.org/wiki/Galileo_Galilei#Name
Surnames are optional in Italy at that time. Galileo is how he refers to himself and how people refer to him.
His name works like "Bostoner from Boston", so it was reasonable for him at the time to refer to himself as just Bostoner.
There are many Isaacs and Alberts. How many notable Galileo(s, not to use Galilei) do we have?
In Italy it's extremely usual to refer to the greatests of the great people of those ages by their given name: Leonardo, Galileo, Dante, Michelangelo. It's testament to their greatness. There is only one Dante that matters, so there is no need to add Alighieri but if you do nobody notices anything strange. It's only a bit redundant. Using only the surname would be unusual.