Hi! Thanks for the kind answers!
I will try to explain better

With "Man of Rohan" I mean like a citizen, or an army member of Rohan. But using the word "Man".
In this case, Rohan is the kingdom of "Lord of the rings" by Tolkien.
About the name "Feardorcha": is it a real irish name? So it doesn't exist a corresponding gaelic name with Frederick?
In fact I read on italian wikipedia that Feardorcha was translated by english people in "Ferdinand" in the past times.
But all other documentation I found say Frederick is Feardorcha.
But I can't understand the process.
In the meanwhile, many many thanks for your help!
Have a happy day
Fede