My favorite character name is still Hiro Protagonist. Nominative determinism at its best. Or maybe they just forgot to update the placeholder name before going to print.

To be fair, Nolan has named a protagonist Protagonist in the past

Isn't that character named as such only in the script with their name never being mentioned in the movie itself?

As far as i know, the film is based on the actual Odyssey (unless they decided to ruin it?) So i don't see why Nolan would do something like this, assuming that it was just another Nolan bad naming scheme make little sense unless you don't know what is the Odyssey (which is kinda strange)