One Piece Chapter 2, page 11: THEY CALL HIM "STRAW HAT LUFFY"

Luffy smiles broadly and declares, "WELL YA SEE... I'M GONNA BE THE KING OF THE PIRATES!!!" Koby is completely dumbfounded, screaming, "K-KING OF THE PIRATES!!!? BUT... YOU'D HAVE TO MAKE THE WHOLE WORLD KNEEL TO YOU!!! WEALTH, FAME, POWER-- YOU'D HAVE TO ACHIEVE IT ALL!!! DON'T TELL ME YOU'RE AFTER GOLD ROGER'S LOST TREASURE, 'ONE PIECE'!!!!!"