monkey d luffy
Luffy 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 Rob Lucci, 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 expanding his blood vessels, which allows oxygen to get to his muscles much faster. Luffy accelerates of 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.[13