AppearanceShanks always wears a long black cape over his shoulders and, until he met Luffy, wore a straw hat that he had worn for many years beforehand. He always wears trousers that are cut below the knee as well as a pair of sandals and is unshaven with a short beard. The most striking thing about Shanks is the color of his red hair, of which his nick-name 'Red Haired Shanks' comes from. He also has three scars across his left eye, which were revealed to have been given to him by Blackbeard, and saving Luffy from a sea king he had lost his left arm. He usually carries a Sabre on his right hip.
At the start of One Piece, Shanks bore much more similarity to Luffy. As Oda's style changed, Shanks began to become more distinct. The shape of his eyes are drawn much sharper. His nose has become more redefined, similar to how Nico Robin's nose is heavily defined from other character's in the series.
PersonalityShanks is one of the most laid back characters in the world of One Piece, preferring to take his time as he and his crew travels around the world rather than rushing from one place to another. Shanks isn't cruel like many other pirate captains, nor does he rule over his crew with fear to gain respect. His friendly nature means he won't purposely seek to harm others, and he is able to make serious characters like Mihawk join in with his fun. Yet despite how simple minded he appears at first, Shanks is a complex person with some rather difficult to understand views. For example, he believes if two people share very different views, its better they go their seperate ways.
Shanks doesn't seem to mind what happens to himself. He'll take others throwing food and drink or spitting on him without even fighting back, laughing with his crew at his own misfortunes. Even losing an arm did not bother him much. However he would never forgive anyone for attacking a friend. 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 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 10 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, he has displayed a side of him that likes to panic when things go wrong.
CrewWhile only a few of Shanks' crew have been named, he seems to generally get along with them all and they look up to him with respect as their captain. Shanks looks out for the well-being of the entire crew, from refusing to take a child (Luffy) on board his ship to denying Rockstar permission to take on Whitebeard's men who had insulted Rockstar's honor.
Of the Jolly Roger Pirates, most relationships between Shanks and the other crewmates remain unknown. However, it has been shown through flashbacks that he would fight with Buggy over just about anything. The Marines themselves described their relationship as a 'brotherly bond' and Whitebeard himself had noted the pair were always together. Shanks appears to still consider Buggy as a friend. He also still refers to Rayleigh as "Master" Rayleigh.
Friends“ Listen up...you can pour drinks on me, you can throw food at me...you can even spit on me. I'll just laugh that stuff off. But...good reason or not...nobody hurts a friend of mine!!!!
-Shanks' warning to Higuma on hurting Luffy. 
Luffy looks up to Shanks as his role model, childhood hero and the man he wants to eventually surpass. At first, Shanks never took Luffy seriously as he was just a boy so mocked his dreams to become a pirate, dubbing him "Anchor". Later after Luffy stood up for him in front of Higuma and his men, as they were leaving when Luffy declared he would be better than him Shanks begins to treat him seriously.
In the manga Ben Beckman tells Shanks that Luffy is going to make something of himself. Shanks confirms this by saying that Luffy reminds him of himself when he was Luffy's age. Just as Luffy is currently looking for Shanks, Shanks eagerly awaits the day he meets up with Luffy. Shanks also sees Luffy as the future for piracy and was delighted at his coming so much he threw a party to celebrate even though he was already suffering from a hangover over being drunk previously. Meanwhile Garp blames Shanks for poisoning Luffy's mind with ideas about being a pirate when he wanted Luffy to become a Marine.
EnemiesThe World Government view Shanks as a problem and a trouble maker, but realizes he is a man who won't try to change the world by himself. However due to the position he holds, they fear he could get out of hand and are prepared to eliminate him if he ever does.
So far, outside of the World Government, the only one who appears to oppose Shanks is Buggy the Clown. Ironically, in their youth Buggy accused Shanks of being too naive and innocent to ever make it as a pirate and yet presently Shanks is a great pirate while Buggy and his crew are quite weak in comparison. As his rivals, the other Yonkou are enemies.