Monkey D. Luffy was born in Foosha Village in the East Blue to his father Monkey D. Dragon and an unknown mother. His father left him in the care of his grandfather, Monkey D. Garp, a vice admiral of the Marines. Garp employed extreme and dangerous training methods in an attempt to make Luffy strong, such as throwing him into deep ravines, leaving him alone in wild territory, and tying him to balloons, but these experiences only hardened the boy's resolve.

As a young child, Luffy was bursting with energy, optimism, and an unwavering ambition to become the King of the Pirates. This dream was ignited and nurtured by his encounter with the pirate captain Red-Haired Shanks and his crew, who docked in Foosha Village when Luffy was seven years old. Luffy idolized Shanks and pestered him daily to take him out to sea. His personality even then was defined by a seemingly carefree and reckless stubbornness, a huge appetite, and a deep, selfless loyalty to those he considered friends. This loyalty was demonstrated when he stabbed himself under the left eye with a knife to prove his courage to Shanks and his crew. That scar remained a permanent mark of his resolve. Shanks later gave Luffy his treasured straw hat as a promise that he could return it when he became a great pirate himself, cementing it as Luffy's most treasured possession and the symbol of his dream.

Luffy's early motivations were simple and pure: to prove himself worthy of Shanks' faith, to become the strongest and freest man on the seas, and to gather a crew of his own. His role in the story during these formative years was to establish the foundation for his entire journey. He was not merely a dreamer; he actively pursued strength and freedom even as a child.

The most important relationships of his youth were forged in the mountains near Foosha Village. Garp entrusted Luffy to the mountain bandit Curly Dadan, who became a harsh but deeply caring maternal figure. Under Dadan's roof, Luffy met his two adopted brothers: Portgas D. Ace and Sabo. The three boys became inseparable, forming a sworn brotherhood by sharing a cup of sake. They trained together, competed fiercely, and swore to set sail and live their lives freely. Luffy's bond with Ace and Sabo taught him the meaning of chosen family and brotherhood, a theme that would define his character forever. The loss of Ace and the separation from Sabo became two of the most emotionally defining events of his life.

Development in his childhood already hinted at his future greatness. He consumed the Gum-Gum Devil Fruit by accident, gaining a rubber body that made him unable to swim but gave him immense potential for combat. He spent his childhood learning to control his newfound elasticity and building his physical endurance through constant scuffles. He was ignorant of books and formal education but possessed an almost supernatural intuition and emotional intelligence, often understanding people and situations far deeper than others assumed. His stubbornness was not just childish defiance it was the unshakable will that would later carry him through impossible odds. He believed that being a pirate meant being the most free person in the world, a philosophy that remained at his core.