PersonalityLuffy is portrayed as a carefree character with great ambitions and a huge appetite. He often thinks with his stomach and eats to the point of becoming comically fat. He is caring and generally good hearted. However, he is not naive and understands most situations more than he shows. He was inspired to become a pirate by his friend "Red-Haired" Shanks who entrusted him with his strawhat, which he holds as one of his most precious objects. Knowing the dangers ahead, he is willing to risk his life to reach his goal, and protect his crew.
He invites several people, such as Chopper or Brook, onto his crew generally for their personality but also because of his instinctual ability to be able to read people. His main reason has been stated a few times in the story. He needs several key jobs filled in his crew (ie: cook, navigator, doctor, musician, shipwright, and so on). Only one member of the crew invited herself on, Nico Robin. She actually has no place on the ship, having no true abilities that Luffy requires. She is just a historian who Luffy accepted. Luffy stated in the beginning of the series that he wants about ten crew members, each with abilities that he feels necessary for his goal. He is rarely concerned with the consequences of his actions, doing what he feels even if it leads to retaliation by a powerful force. However, he is an extremely loyal captain, who has demonstrated at many points throughout the series that he is willing to risk his life for the well-being of his crew.
Eating the Gum-Gum Fruit gave his whole body the properties of rubber, which makes him virtually immune to all blunt force attacks (including the round flintlock bullets used in the One Piece universe). The fruit also gave him the ability to stretch at will. Combined with the elasticity of his body, he uses that ability to accelerate parts or the whole of his body as if shot by a slingshot to deliver punches, kicks, headbutts, body checks, or simply for propulsion. But like everyone who consumed a Devil Fruit, Luffy is unable to swim and when drenched in sea-water or in contact with an artifact blessed by the sea quickly loses his strength. He also has great physical strength as he was able to knock over 2 large apartment buildings at the same time (Water 7 arc).
After being effortlessly beaten by Admiral Aokiji, later in the series, Luffy develops two techniques to improve on his rubber abilities. The first of these he calls Gear Second. He activates it by accelerating the flow of his blood by using his legs as pumps. When this happens, the blood flowing rapidly through his body creates friction, heating up his body and makes his skin glow and produce steam. This increases his attack power and overall speed, but drains his stamina and if overused makes him temporarily unable to move afterward, as well as shortening his life span. The second is Gear Third, which is activated by biting a hole into his thumb and blowing air into his bones. He is then able to move the air around his bone structure and strike with limbs comparable in size to those of giants. The side effect to using Gear Third is that Luffy temporarily shrinks to a fraction of his normal size after releasing the air for a length that corresponds to the amount of time he was using Gear Third. He is capable of using both techniques simultaneously.
Even further into the series, Luffy demonstrates the still innate ability to use Haki (覇気?, lit. ambition) to make people or animals in his proximity faint. He has a very rare variation of Haki, which he shares with Boa Hancock. He first used it on Motobaro without realizing what he did.
In the start of the series Luffy sets out to sea in search of One Piece, the treasure supposedly left behind at the end of the Grand Line by the deceased King of the Pirates, Gold Roger. During the first leg of this journey, crossing his home sea, called East Blue, he acquires his first ship, the Going Merry and a basic crew, consisting of the swordsman Roronoa Zoro, expert navigator and thief Nami, the liar Usopp and the first-class chef Sanji, together known as the Straw Hat Pirates. But he also meets opposition. After defeating the most notorious pirates of East Blue, Buggy the Clown, Captain Kuro, Commodore Don Krieg, and the Fish-man Arlong, he is placed on top of that sea's wanted list with a bounty of thirty million in the fictional world's currency, Berry.
After entering the Grand Line, he agrees to bring the princess of Arabasta, Nefertari Vivi, safely into her homeland to stop a rebellion, incited by a member of the Seven Warlords of the Sea, Sir Crocodile. On the way there, Luffy defeats member of the world government, King Wapol of the Drum Empire, and finds his crew a doctor in the person of Tony Tony Chopper. In Arabasta, Luffy defeats Crocodile and ends the civil war. The world government, to whom the Warlord's betrayal and defeat is equally embarrassing, covers up the involvement of the Straw Hats and raises Luffy's bounty to 100 million Berry. And upon leaving the country, Luffy allows Robin to join his crew.
Leaving Arabasta kingdom, the crew encounter a gigantic ship falling out of the sky, and eventually find out about, and then journey to, the cloud island Skypea. There, Luffy and the crew encounter two races of people with wings who have been engaged in a unceasing war for 500 years, and who are ruled by a man known as "god". Breaking the law almost immediately upon entering, everyone eventually fight back against the corrupt "god" Enel and over throw his rule, bringing an end to the war, and acquiring many friends and gold. As this adventure was not reported to the marines, the crew's respective bounties remained unchanged.
After returning to the surface, Luffy defeats the pirate trickster Foxy the Silver Fox and encounters one of the navy's top fighters in Admiral Aokiji, who has a personal interest in Robin. Aokiji single handedly defeats the crew's top fighters but lets them escape to honor a promise and to repay a debt. But the lost fight has other consequences as it demonstrates the crew's vulnerability and Robin's danger to them.
The crew then travels to an island called Water 7, which is an island floating on water. There they meet shipwrights from all over the world. However, Robin leaves the crew to assassinate the president of the shipwright company. The Straw Hat Crew is framed, and Robin is then taken by CP9. The Straw Hat Crew then chase after CP9 and end up at Enies Lobby, the World Government Center. The shipwright, Franky, also decides to join the fight. After many battles with members of CP9 and World Government, the Straw Hat Crew ends up beating the CP9 and claims Robin as an official crew member. They then travel back to Water 7, where they get a new ship called Thousand Sunny made by Franky. Franky joins the crew, and becomes the crew's shipwright. After the final battle, in Enies Lobby, all of the crew members receive their own bounty; Luffy´s bounty having been increased to 300 million Berry.
The Straw Hat Crew then decide to enter the New World by passing the Red Line. Before entering it, they must pass through the Florian triangle on their way to Fishman Island. After entering a dense fog, the crew come across a ghost ship inhabited by a living skeleton called Brook. The Straw Hat Crew then find an island ship called Thriller Bark. The captain of this ship is Gecko Moria, one of the Seven Warlords of the Sea, whose crew consists of hundreds of zombies. The crew assist Brook in defeating Gecko Moria and returning his shadow to him. After freeing the rest of the islands prisoners, Brook agrees to join Luffy and his crew.
The crew then went to Sabaody Archipelago to find a coating engineer to coat their ship so that they would be able to proceed to Mermaid Island. However, one of their guides, a mermaid, gets captured and is to be auctioned off to the highest bidder. The crew find the venue for the auction and attempt to buy the mermaid back only to have it backfire when one of the Celestial Dragons bids an unbeatable amount. This then helps cause an incident in which an enraged Luffy sends one of the Celestial Dragons flying, causing chaos to fall upon the Sabody Archipelago. As the crew attempts to escape, they encountered Kizaru, another Marine admiral and Bartholomew Kuma, a Warlord. Bartholomew Kuma then uses his ability to send all the crew members to different islands. The island that Luffy lands on is ruled by Boa Hancock, the only female Warlord. Boa Hancock eventually falls in love with Luffy and helps bring Luffy to Impel Down, a marine prison, to save his brother, Portgas D. Ace who is imprisoned there after having been defeated by Blackbeard.
Luffy, breaks into the prison, and fights his way down all five of the levels of impel down (each of which is characterized by a different type of punishment), acquiring allies as he progresses. Impel Down's guards and warden hear of his actions, and move to stop him, which results in Luffy being defeated by the Warden. Luffy, failing to break Ace out of prison in time, fights his way back out of the prison, creating a massive breakout from Impel Down, the first one in its history, in order to follow Ace to the Holy Land Mariejois to stop his execution. Backed by Jimbei (a former Warlord), Emporio Ivankov (former ruler of Kamabakka Kingdom), Crocodile, Buggy, and a large amount of the now free prisoners of the Down, Luffy arrives at the site of Ace's execution and starts participating in an epic engagement between Whitebeard's forces and the Marines.