A straw hat can refer to any brimmed hat that is woven out of straw.
One straw hat is particularly famous, having been worn by Gol D. Roger and Shanks. It is now worn by Monkey D. Luffy, giving him his epithet "Straw Hat Luffy", and the namesake and symbol of the Straw Hat Pirates and Straw Hat Grand Fleet by extension.
Gol D. Roger/Shanks/Monkey D. Luffy
Monkey D. Luffy's straw hat is the main symbol of the entire series and is the origin of his nickname "Straw Hat Luffy." His straw hat was given to him by his idol, Red Hair Shanks when Luffy was a child, and he promised to give the hat back to Shanks once he becomes a great pirate (or in other words, the Pirate King). Much later, during the Straw Hat Pirates' departure for Fish-Man Island, it was revealed by Silvers Rayleigh that this straw hat originally belonged to Gol D. Roger.
Although Luffy's straw hat is his treasure, he is seen without it on occasion. This is usually because he does not want anything bad to happen to it, in which case he usually gives it to another member of his crew for safekeeping. It has been damaged twice in the manga canon. The first time it was damaged by Buggy when he was fighting Luffy. Buggy spat on the hat as well when he learned that it previously belonged to Shanks. After the fight, Nami repaired it for him. However, Luffy was overjoyed that Nami had repaired it, resulting in Luffy poking it several times, accidentally making another hole in the repair work. This caused Nami to hit him with the sharp end of the needle, since the repair had only been temporary. Nevertheless, she repaired it again.
During the Alabasta Arc, when Ace leaves the Straw Hats and Vivi, he gives Luffy a "blank piece of white paper". After saving the vivre card from getting eaten by Matsuge, Nami sews it on the inside of the red band around the circumference of Luffy's hat. After the arc, the hat was also given a string, so that Luffy could wear it securely on his person and would not have to worry about losing it.
During the Marineford Arc, Luffy's hat fell off when Jinbe, who was carrying him, was struck by Admiral Akainu. As Luffy was mentally shattered from his brother's death, he did not notice the hat falling off, nor did Jinbe, who was occupied with dealing with the Admiral. After Shanks appeared, the straw hat was temporarily reunited with its old owner after over ten years. Shanks convinces Buggy to return the straw hat to Luffy, resulting it to end up in Trafalgar Law's temporary care. The straw hat was then handed over to Rayleigh, who in turn returned the straw hat to Luffy after he recovered. Prior to his training with Rayleigh at Rusukaina Island, Luffy set aside the hat on the island's only safe location. Luffy picked the straw hat back up after the training was over.
Occasionally, Luffy may overlap the straw hat with another piece of headwear, either as a disguise (since he refuses to put the hat away), as a necessity, or as a part of fashion.
For his initial disguise during the Whole Cake Island Arc, Luffy overlapped the hat with what appears to be a white turban. Though he lost it during his fight against Charlotte Cracker. Later, after receiving a change of clothes from the Fire Tank Pirates, he overlapped the straw hat with a black fedora with a white band. He removed it after defeating Charlotte Katakuri.
During the non-canon G-8 Arc while in the disguise of a cook, Luffy stretched a white chef's hat over the straw hat in Episode 197, until Sanji removed it for him in Episode 200, after their cover was blown.
In Chopper's Kingdom on the Island of Strange Animals, when Luffy attempted to disguise himself as an animal, he tied a couple of leafy ranches to his hat with a cloth, in order to (poorly) duplicate horns.
In One Piece: Stampede, Luffy placed an oversized bulbous brown hat atop the Straw Hat, which he got during the Pirates Festival. The hat had a bulb-like shape with a wavy rim, mainly light brown in colour, and has a dark-brown triangle design band around the widest part.
The kasa (conical straw hat) made by Ace was given to Oars Jr., as he believed it would help the giant since he was so close to the sun. Oars Jr. was so moved by this gift, he fought with all of his strength to save Ace during the Battle of Marineford.
In a poor attempt to impersonate Luffy, Demaro Black wore a straw hat. However, his straw hat was different as it was frayed and unkempt, with a flat top rather than a domed one, and a striped band around its circumference. It fell off when Sentomaru smashed him on the head.
Fish-Man Island Children
After Luffy and his crew defeated the New Fish-Man Pirates and saved Fish-Man Island, the children of Fish-Man Island wanted to get straw hats so they could play hero. Despite the adults saying that straw hats can only be bought on the surface, Jinbe stated that he would pick some up for them. After obtaining the hats, the children were rejoicing.
Dressrosa Children and Tontatta Dwarves
Mary Geoise's Straw Hat
- In the game Pirates of Black Cove, one of the unique items that can be acquired is Luffy's straw hat, which lowers the damage one receives in battle by a little bit.
- In the game King's Bounty: The Legend, and in its sequels, a player can acquire a similar straw hat with red ribbon. It boosts the leadership of the hero. It was confirmed as an Easter Egg with a nod to One Piece in the official forums by a representative of the developers.
- As part of a promotion from July 22 to July 29 2019, in celebration of its fifth anniversary and the twenty-second anniversary of the One Piece manga, players of the game Pokémon Go received a Pikachu that is wearing Luffy's straw hat.