There are few things more iconic in One Piece than Monkey D. Luffy’s Straw Hat. The hat is one of his most prized possessions. He's rarely seen without it and has only allowed just a few people to hold or touch it. The prolific pirate has even gone to extreme lengths to protect it from getting damaged or dirtied. It holds such an important place in Luffy’s heart that he even chose it as the name and symbol of his pirate crew.
Shonen heroes can be a very idiosyncratic bunch, so the fact that Luffy has a thing for straw hats might be brushed off by some as a quirky character trait. However, a deeper reading of the manga reveals that this particular straw hat is much more than a cool fashion accessory that coordinates well with his red vest and blue pants. The hat has a long history with a direct and strong, albeit obscured, influence on who Luffy is and what he wants to accomplish.
As presented in the very first chapter of the series, the hat was gifted to Luffy by Shanks just prior to him setting off on an adventure that would ultimately result in his coronation as one of the Four Emperors of the New World. As a young boy, Luffy idolized Shanks and wanted to follow in his footsteps as a pirate. While ignoring his pleas to go on adventures with him, Shanks grew to respect Luffy and the two developed a brother-like friendship. Indeed, In One Piece #1, Shanks saves Luffy a couple of times, and even loses half of his arm rescuing from a shark. Ultimately, just as he is about to set sail, Shanks gives the straw hat to Luffy as a way of encouraging him to follow his dreams. As Shanks made clear, he wanted the hat back, when Luffy became a great pirate. At that point in time, Shanks is a good but not great pirate, so his reference to “great pirate” must surely have been to his old captain Gol D. Roger.
Later in One Piece #603 fans learn that before the hat comes into Shanks's possession, it belonged to a young Gol D. Roger, who at the time, looked strikingly similar to Luffy. Roger went on to become the one and only Pirate King and the last person to hold the “one-piece” treasure that gives the series its name.
Shanks was a young member of Roger’s famous Rogers Pirates crew during their successful campaign to take over the Grand Line and become the fiercest band of pirates in the world. At some point during these adventures, Shanks came into possession of the straw hat. By all accounts, he kept the hat until he gave it to Luffy, who was about the same age as Shanks when was first seen wearing the hat. There is no explanation of how Shanks got the hat, but a common belief among fans is that Rogers gave it to Shanks similar to how Shanks gave it to Luffy.
An element of Luffy’s care for the hat surely has something to do with his admiration of Shanks. However, over his years of pirating, Luffy most certainly learned of the hat’s backstory. Accordingly, his protection of the hat must also be because it represents a link and bond to a line of common men who went on to become the great pirates. It foreshadows a positive end to Luffy's story. Indeed, if this One Piece legacy holds, Luffy’s possession of the hat suggests his eventual rise to great pirate status.