As I said, in the original comics Mendoza's only characteristics were his mustache, the fact that he only said his own name, and that Partner really, really hated him. That gave me a bit of pause in the remake, because fleshing him out or dropping him for a new villain were equally viable options.
At first I played around with the idea of making Mendoza like Arsene Lupin, but with the whole "gentleman" part of his character being a pastiche on the modern take on it these days. I didn't stick with that idea, it seemed to dense and would likely need to take too much time away from Action Hat and Partner to set up.