One Piece Chapter 1.1, page 40: Romance Dawn (Version 1)

Luffy lands on the deck of the pirate ship, causing it to shake. Gyari and his crew stagger, startled: "UOH!? WHAT!!?" and "CAPTAIN...!!" and "WHAT IS IT!!". Luffy stands proudly on the railing, crossing his arms. Gyari screams in shock, "GEH!!!". Luffy grins confidently and replies, "IT'S NOT GEH. MY NAME'S LUFFY."