In the Brazilian subtitle, he was first called as Ruffy, but in the half of Enies Lobby/Water 7 Saga he started being called as Luffy, so I'm interested in knowing what is his name.
His name is Luffy. You better know his name when he becomes King of the Pirates!
We have discussed the difference with regard to pronounciation on this site before.
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Note that I answered this rather than marked it as a duplicate because this question is about spelling, not pronounciation. It is not, therefore, a true duplicate. – kaine Jul 8 '14 at 12:38