Monkey D. Luffy, known as Ruffy in the Latin American Spanish dub, is the main protagonist of the anime and manga series One Piece. He was born in Foosha Village on the East Blue Sea and as a young boy accidentally ate the Gum-Gum Fruit, a Devil Fruit that gave his entire body the properties of rubber at the cost of his ability to swim. Inspired by the pirate captain Red-Haired Shanks, who saved his life and gave him his signature straw hat, Luffy decided to become a pirate at the age of seven. He made a promise to Shanks that he would become a greater pirate than him and one day return the hat. After ten years of training, Luffy set sail from his home island with the goal of finding the legendary treasure One Piece and becoming the King of the Pirates, which he understands as the freest person in the world.

Luffy is typically carefree, cheerful, and impulsive, with an enormous appetite that often leads to comedic situations. He speaks his mind openly and rarely plans ahead, yet he possesses a sharp situational awareness and a deep, instinctive understanding of people and their true intentions. Beneath his goofy exterior, Luffy is fiercely loyal to his friends and crewmates, and he will risk his life without hesitation to protect them or help those he considers allies. He despises injustice and cruelty, often stepping in to liberate oppressed people even when it brings him into conflict with powerful enemies.

His driving motivation is the pursuit of absolute freedom, symbolized by his quest for the One Piece and the title of Pirate King. He does not seek wealth or power for their own sake; instead, he wants the ability to live as he pleases and to have a crew of trusted companions who share his adventurous spirit. Luffy values bonds of friendship above all else, and he is known to inspire fierce loyalty in everyone who travels with him.

As captain of the Straw Hat Pirates, Luffy is the central figure of the story. His decisions and actions propel the narrative forward, drawing his crew into epic confrontations with the world's most powerful forces, including the Marines, the Seven Warlords of the Sea, and the Four Emperors. He builds his crew gradually, recruiting each member after winning their trust and respect. Key relationships include his first crewmate Roronoa Zoro, his navigator Nami, the sniper Usopp, the chef Sanji, the doctor Tony Tony Chopper, the archaeologist Nico Robin, the shipwright Franky, the musician Brook, and the helmsman Jinbe. His family ties are significant: his father is Monkey D. Dragon, leader of the Revolutionary Army; his grandfather is Vice Admiral Monkey D. Garp of the Marines; and he considers the late Portgas D. Ace and Sabo as his sworn brothers.

Over the course of the story, Luffy undergoes substantial development. Early defeats and personal losses, especially Ace's death, force him to mature and recognize his own limits. He trains intensely for two years under the guidance of Silvers Rayleigh, learning to master the three forms of Haki: Observation Haki, Armament Haki, and the rare Conqueror's Haki. He also refines his Devil Fruit abilities into a series of transformations called Gears, each granting new levels of power. Gear Second increases his speed and strength by accelerating his blood flow; Gear Third inflates parts of his body to gigantic proportions; Gear Fourth combines his rubber body with Armament Haki to create massive, powerful forms such as Boundman, Snakeman, and Tankman. Later, it is revealed that his Devil Fruit is actually the mythical Human-Human Fruit, Model: Nika, and its awakened form, Gear Fifth, grants him the ability to fight with cartoon-like freedom, stretching reality itself. Through his growing strength, Luffy defeats some of the world's most dangerous pirates and Marines, earns a bounty of three billion berries, and eventually becomes one of the Four Emperors of the Sea, placing him among the most influential figures in the world.

Luffy's notable abilities stem from his rubber physiology. He can stretch his limbs, torso, and even internal organs to incredible lengths, granting him immense reach and flexibility. He is immune to electricity and blunt impacts, though he remains vulnerable to sharp objects, extreme temperatures, and drowning. His signature moves include the Gomu Gomu no Pistol, a long-distance punch; the Gomu Gomu no Gatling, a rapid barrage of punches; and the Gomu Gomu no Bazooka, a two-handed thrust. Combined with Haki, he can deliver devastating attacks like the Gomu Gomu no Red Hawk, which ignites his arm, or the Gomu Gomu no Kong Gun, which incorporates Conqueror's Haki. As his journey continues, Luffy's abilities and influence grow, cementing his role as a transformative force in the world of One Piece.