lol ok.
the OC above is supposed to be from a lorean manhwa called Demon Diary. In the plot, there are many Demon Lords that rule over a plot of land each (only on the...West side of the continent...i think. it was either west or east). And the ruler of each plot of land is a called a Lord.
The "III" after Galatea's name indicates that she is the third generation to take on the name "Lord Galatea". All successive Lords to take on a plot of land has a certain name that is passed down to their heirs, along with any knowledge and power they have. In this case, the name "Galatea" was passed down.
And so...that's how she's called a "Lord".
Well, i'd recommend reading it for the awesome art, not the plot..as it kinda veers off course after the first few chapters as the original writer for the story had exams and school to worry about, so the writer was changed around.