Luffy was born in Foosha Village in East Blue. When he was seven years old, he met and befriended a crew of pirates led by an affectionate captain named Red Haired Shanks. Luffy, inspired by them, decided to become a pirate as well.
During an incident with a local bandit, Luffy accidently eats the Gomu Gomu no Mi fruit, which transforms his body into that of a Rubber Man. Initially, this situation affects Luffy badly as it means he will never be able to swim again, which is a great weakness to anyone who wishes to journey the seas. This, however, does not deter Luffy's dream and he continues aspiring to become a pirate.
Soon after, Luffy is introduced to two men whom he would eventually call brother, Portgas D. Ace, and Sabo. During an incident with pirates hired by Sabo's brother, Sabo is seemingly killed, and Ace then leaves the island shortly afterwards to become a pirate.
During the next three years, Luffy would hone his skill with his new found rubber abilities, and then set off on his own to become the King of the Pirate. Along the way, he befriends many people, and adds people such as Roronora Zoro, Usopp, Nami, Tony Tony Chopper, Franky, Nico Robin, and Brooks to his crew.
Luffy's fame grew with each member he added to his crew, as well as each problem he created for the World Government, eventually earning himself a $400,000,000 bounty. Of course, his adventures are still on going, and wherever Luffy goes, you can be sure that a fair amount of fun (in his mind) will be had.