The most striking thing about Shanks is the color of his red hair, from which his epithet 'Red-Haired Shanks' is derived. He also has three scars across his left eye, which were revealed to have been given to him by Blackbeard, He is also missing his left arm, a direct result of him saving Luffy from a Sea King when Luffy was a child. The scars across his left eye seem to tingle whenever he confronts Blackbeard.
At the start of One Piece, Shanks bore a physical similarity to Luffy. As Oda's style changed, Shanks became more distinct. The shape of his eyes are much sharper and narrower than they used to be. His nose has become more defined, similar to how Nico Robin's nose is heavily defined compared to those of most other characters in the series. His trademark red hair is also slightly longer, with the fringe pushed more toward the sides. It is also wavier and more slicked back, as opposed to how it was parted in the middle at the beginning of the series.
Shanks is an extremely laid-back man, preferring to take his time as he and his crew travels around the world rather than rushing from one place to another. Shanks is not cruel like many other pirate captains, nor does he rule over his crewmembers with fear to gain respect. His friendly nature means he will not purposely seek to harm others, and he is able to make serious people like Dracule Mihawk join in with his fun. However, despite how simple-minded he appears at first, Shanks is a complex person with some rather difficult-to-understand views; for example, he believes that if two people share very different views, it is better that they go their separate ways.
Shanks does not seem to mind what happens to himself; he will take any insults and humiliations directed at himself without fighting back, and will simply laugh it off with his crewmates. Even losing an arm did not bother him much. However, he would never forgive anyone for harming his friends.
Shanks and his crew are almost always seen partying and drinking alcoholic beverages whenever they make an appearance, as the captain's favorite pastimes are attending and hosting parties and banquets. According to Oda, Shanks is the one character that resembles himself the most out of all the One Piece characters, because of his fun-loving partying nature and cheerful personality.
He also is against the idea of needless bloodshed, even if honor is involved, and so far seems to only step up for a fight when a friend is in danger. He also seems to admire those who have courage, having protected and commended Coby for gathering his courage to stop the war as the young Marine believed that it was pointless to continue.
Shanks also has skills in diplomacy, as shown when he brokered a ceasefire between the Whitebeard Pirates and the World Government. His skills in diplomacy are so great that he managed to convince Sengoku to agree with his proposition, even though Sengoku has a strong hatred for pirates.
He also likes teasing people, as demonstrated by his apparent reactions to Luffy as a child. Oda also stated that if a child asked Shanks for a Devil Fruit, he'd tease them about being ten years too young to eat one. Shanks himself was like Luffy (as a child) in his younger years.
Despite being calm and brave most of the time, Shanks sometimes reacts in ways that are not always fitting in what others expect from him, a trait noted by Buggy as having "always annoyed him". These include panicking when things go wrong or shrugging off Buggy's angry disposition towards him to greet him in a friendly manner. He also seems to carry something personal regarding Marshall D. Teach deep within him, as when he spoke about his 3 scars to Whitebeard, he became serious about the situation surrounding Teach.
Even though he has traveled the world, Shanks believes the best sake can be found in his hometown in the West Blue. When with Whitebeard, he also refers to alcohol as "healing water".
Like other characters in One Piece, Shanks has his own unique laugh, starting it with a "Da" (i.e. Dahahahahaha!).