From Viz:
As a child, Monkey D. Luffy was inspired to become a pirate by listening to the tales of "Red-Haired" Shanks. But his life changed when Luffy accidentally ate the Gum-Gum Devil Fruit and gained the power to stretch like rubber at the cost of never being able to swim again. Years later, still vowing to become the king of the pirates, Luffy sets out on his adventure one guy alone in a rowboat, in search of the legendary "One Piece," said to be the greatest treasure in the world.

The best-selling manga in history and tied with Superman for the best-selling comics in history.

Note:
Because a takedown notice was sent to MangaDex from the owners of this series, English fan translations of One Piece are unable to be posted at this time. The series can be read in its entirety at the official Shonen Jump website, with the first and latest three chapters available at any time and the rest accessible with a Shonen Jump membership (which costs about $2 a month and can be accessed via a VPN if you are outside the US).