Monkey D. Luffy ( LOO-fee) (Japanese: モンキー・D・ルフィ, Hepburn: Monkī Dī Rufi, [ɾɯꜜɸiː]), also known as "Straw Hat" Luffy, is a fictional character and the protagonist in the Japanese manga series One Piece created by Eiichiro Oda. Luffy made his debut as a young boy who acquires the properties of rubber after accidentally eating one of the Devil Fruits.

Monkey D. Luffy is the captain of the Straw Hat Pirates, and dreamt of being a pirate since childhood from the influence of his idol and mentor Red-Haired Shanks. At the age of 17, Luffy sets sail from the East Blue Sea to the Grand Line in search of the legendary treasure, One Piece, to succeed Gol D. Roger as "King of the Pirates".

He fights multiple antagonists, and aids and befriends the inhabitants of several islands on his journey. Usually cheerful, he becomes serious and even aggressive when he fights. Luffy uses his rubber body to concentrate his power, executing a range of attacks. In his signature attack, the Gum-Gum Pistol, he slingshots punches at opponents from a distance. Luffy also grows stronger over the course of the story by transforming his body through different "Gears;" this is reflected in his bounty, which is used to measure the threat he poses to the World Government. He is the grandson of Monkey D. Garp, who is a vice-admiral of the Navy; the son of Monkey D. Dragon, who is the leader of the Revolutionary Army; and sworn brother of Portgas D. Ace and Sabo.

Luffy appears in most episodes, films, television specials, and OVAs of the manga's anime adaptations, as well as in several of the franchise's video games. Due to the series' international popularity, Luffy is one of the world's most recognizable manga and anime characters. Beyond the One Piece franchise, the character also appears in various manga, anime series, and collaborative video games. His critical reception has been largely positive.