Monkey D. Luffy, commonly known as "Straw Hat Luffy" or simply "Straw Hat", is the founder, captain, and strongest combatant of the increasingly infamous and powerful Straw Hat Pirates. He fearlessly pursues the legendary treasure of the late Gol D. Roger in order to become the new Pirate King and reach a further, untold dream (currently known to only his crew, family and closest friends). He believes that being the Pirate King means having the most freedom in the world.

Born on Dawn Island, Luffy is the son of Revolutionary leader Monkey D. Dragon and grandson of the Marine hero Monkey D. Garp and as such is a member of the Clan of D. Most of his childhood was shaped by Garp and Curly Dadan, under whose care he befriended and swore brotherhood to the late Portgas D. "Fire Fist" Ace and Sabo. However, he draws his greatest inspiration from the pirate "Red-Haired" Shanks, who (unwittingly) enabled him to eat the Devil Fruit that turned his body into rubber, sacrificed an arm to save his life, and gifted his signature straw hat as a symbol of their vow to reunite someday, after Luffy became a great pirate.

As a pirate, Luffy has actively opposed countless regional, national, and global powers, beginning with several established East Blue pirates and extending to the Marines, the Seven Warlords of the Sea, Cipher Pol, the World Nobles, and even the Four Emperors of the New World. Despite his young age and relatively short career, he has triumphed over a majority of these, successfully invading and indirectly causing the annihilation of Enies Lobby, escaping the impregnable Impel Down, enabling several key developments in the Summit War of Marineford, and defeating three Warlords and an Emperor in direct combat. At the same time, he carries a great penchant for attracting friends and allies; in addition to personally engaging every member of his crew, he has earned regard and gratitude among many nations, fellow pirates, the Revolutionary Army, and even several Marines.

Luffy has gained wide infamy through his accomplishments, heritage, and general recklessness, drawing many large bounties as well as the focused hostility of the World Government, Marine Headquarters, and Fleet Admiral Sakazuki in particular. Currently, he is recognized as a central member of the Worst Generation, the unwilling leader of the seven-crew Straw Hat Grand Fleet, and—in wake of defeating Kaidou during the Raid on Onigashima—one of the Four Emperors, with a bounty of 3,000,000,000. Since the awakening of the Gomu Gomu no Mi after centuries, Luffy has also been heralded by a few as the second coming of Joy Boy, as well as the next Sun God Nika.

He is the main protagonist of the One Piece manga and anime series.