Luffy is renowned for wearing his trademark Straw Hat (in which he gets his nickname 'Straw Hat Luffy' from) which was given to him when he was young by the legendary pirate captain Red-Haired Shanks. His outfit includes short trousers and sandals, and a red vest. Luffy has a scar underneath his left eye, which he caused in order prove he is mature and is not afraid of pain and short black hair.

At first glance, Luffy does not appear to be very intelligent. However, because he views the world in a straightfoward and simple manner, he is occasionally the only person who can see past the events and see what should be done. He sees the world in a childish manner.

Although Luffy is fairly lightheaded and a funny character, he has an unstoppable sense of determination, optimism and commitment and will do anything to stand up for his friends and comrades. Luffy is simple-minded and can easily be amazed by the simplest things. He likes to make fun of other's imperfections and character traits, despite the fact that he is usually worse than them. Luffy seems to have an unstoppable appetite, a characteristic that is common to the Japanese archetype of the (at times simple-minded) young male hero/adventurer with a heart of gold; perhaps the hunger more so in Luffy's case. One comical scene involved him eating an entire wheelbarrow full of fruit in the blink of an eye, followed by Zoro and Sanji loudly dismissing the spectacle as some kind of trick. He also seems to have little to no fear, only truly fearing his grandfather to the point that he does not fight back and is intimidated at the mere mention of him. Along with that, he has great courage to back it up as well as unbelievable strength. Ever since consuming the devil fruit he was shown to be not worried about his inability to swim, much like his brother. An example of this is because when they are sailing he can usually be found on the bowsprit of the Going Merry, he calls this his "special seat" and is usually hanging off of it without minding the danger of falling overboard. Much of these traits are common among Ds.

Luffy is the captain of the Straw Hat Pirates and is best friends with all of them and values them over all else. They are all usually annoyed by his immaturity and stupidity but they all respect him for his qualities as a natural-born leader and his strength. All the members of the Straw Hat Pirates have complete faith and trust in Luffy, even if they often scold him for doing something thoughtless. Despite almost always being clueless and happy, in serious battles and whenever someone threatens his crew or if they are in danger he will become incredibly enraged and serious and gains a distinct killer instinct.

Luffy never kills any of the villains, no matter how cold-hearted they are; instead, he frequently sends the villain flying, knocking them out or until the point that they are almost near death, which results in some of the villains searching for revenge, such as Buggy the Clown and Alvida. Oda explains that it's not a question of morality so much as a matter of punishing the villains for their crimes - he feels that killing the villains lets them off too lightly, whereas he considers letting them live to see their dreams be ruined a far more fitting punishment.

Luffy's dream is to find the One Piece and become Pirate King. He knows that to achieve his goal, he will have to defeat many strong opponents, including the World Government and his childhood hero Shanks. He is not frightened by this, but anticipates the fight.