Red Hair Pirates

The Red-Haired Pirates are a strong crew ruling over the New World', led by Captain Red-Haired Shanks. This crew is responsible for influencing two of the Straw Hats to become pirates, Luffy and Usopp.

Part in the story
The Red Haired Pirates are the first pirate crew to appear in the series and are the main influences of both Luffy's and Usopp's journeys. Ten years before the present time line, they spent a year in Luffy's hometown and became very good friends with Luffy, which led to him wanting to become part of their crew. However, Shanks told him that he was too weak, which angered him. Shanks was also the one who, unintentionally, supplied Luffy with his Devil Fruit. When a group of mountain bandits hassled the crew in a bar, they didn't fight back, but once they left, they immediately burst out laughing, saying that pirates are cowards. Luffy was angry at them for not fighting back, since he did not realize that there was no need to.

Later, after the bandits showed up again when the crew were away, Luffy overheard them saying bad things about Shanks and his crew so Luffy's temper flared up and started insulting their leader, Higuma. The bandits easily subdued him and wanted to kill him. Then Shanks and his crew arrived and immediately took control of the situation, easily beating all of the bandits. However, the leader, Higuma the Bear, had escaped out to sea in order to kill Luffy, only to be eaten by a Sea King. Since Luffy could not swim due to his Devil Fruit, he began to sink into the water, but Shanks quickly saved him. Because the Sea King was about to eat Luffy, he dodged it but his left arm was torn off. Shanks shows no regret of this, even saying to Whitebeard he was making a bet on the New World. He frightened the monster off simply by staring at it and saying "Get lost". Later, when the crew finally decided to leave, Luffy said he didn't want to join Shanks and his crew anymore. Luffy said that he would be a pirate on his own, which Shanks then said that there was no way that he could become a pirate. Luffy immediately declared his intentions to become an even greater pirate than Shanks and to become the Pirate King, so an amused Shanks gave his signature straw hat to Luffy, which he said to give back to him once he surpassed him.

Usopp's connection to the Red Haired Pirates is through his father, Yasopp. When Usopp was young, Yasopp left his family in order to go out to sea, as urged by his wife. Due to how he was raised, Usopp understood that his father left to pursue his dream and harbors no ill will against him--in fact, he wants to become a great sniper and man of the sea like him.

They make their first appearance in the present time line after Luffy gets his first bounty, and as a result, they celebrate Luffy's arrival in the world of piracy. Later on, they contact Whitebeard for unknown reasons, though it seems to somehow relate to Portgas D. Ace and Blackbeard. The World Government fears that the two crews may end up joining together, but have decided to simply observe their actions for now.

Later, in the WhiteBeard War, they are seen upon reaching Marineford, as Shanks stops Admiral Akainu from killing Coby, and Beckman stops Admiral Kizaru form shooting his light laser, as they're about to stop the war.

Crew strength
The strength of the crew as a whole is unknown. But Rockstar, a recent addition to Shanks' crew, has a bounty of 94,000,000 and is still considered to be a rookie. While the bounties of many of Shanks' other crew members are still unknown, if Rockstar's bounty is any indication to go by, their crew is indeed very strong.

The first hint at their crews strength came early on in the story from Luffy's past. The bandit leader Higuma the Bear tried to threaten Shanks with his 8,000,000 bounty, but Shanks' was not afraid of the man and even took having a bottle of sake and his plate of food being smashed and spilled over him. Later on, Benn Beckman took on the bandits men and wiped them all out with ease, telling Higuma that if he and the bandits wanted to take them on they should bring a warship as a back-up. Moments later, Shanks did something shocking while rescuing Luffy from the sea - he scared away a Sea King just by staring at it.

When Mihawk, one of the Shichibukai, brought news of Luffy's rise to fame, the younger, weaker members of his crew appear terrified of the great swordsman and approached him with caution. However, the senior members (including Shanks, Benn Beckman, Yasopp and Lucky Roo) appeared not bothered at all by his visit. This is possibly because of their captain's friendly relations with him, but it's also likely that this is because they are around his league as well.

Shanks does not fear Whitebeard, the world's strongest rated pirate, whereas some pirate captains quiver at the mere mention of his name. Rockstar also used his captain's name to plea to Whitebeard the importance of a letter he delivered to him.

The final clue to the crew's strength is that the World Government greatly fears what would happen if the Red Haired Pirates and the Whitebeard Pirates joined up. Both Shanks and Whitebeard are among the Yonkou.

Other Information
Not much is currently known about the Red Haired Pirates. Shanks used to be on the same crew as Buggy the Clown, and Buggy forever hates him for botching one of his treasure hunts by "making" him eat a Devil Fruit (though it was really entirely his own fault).

While the Red-Haired Pirates appear in only small scenes normally at the end of arcs, they seem to be an ongoing background plot throughout the entire story. They are a very laid back band of pirates who are almost always seen partying and drinking alcoholic beverages whenever they make an appearance. They seem much friendlier compared to other pirate bands seen in the series: they hung around Luffy's hometown for roughly a year without complaints from the local villagers (aside from the ones that came from Mayor Woop Slap).

They have intercepted the attack of Kaidou, another Yonkou against Whitebeard. It is unclear whether they are actually fighting against each other or only blocking the path.

Recently, the crew arrived at Marineford, with the intent of ending the Whitebeard war. By proposing an agreement with Fleet Admiral Sengoku, the war was thus ended.

Trivia

 * The Jolly Roger of the Red-Haired crew is similar to the flag of Calico Jack with 3 scars added to it. However, Calico Jack's flag is generally a fairly popular pirate reference, and since Oda has never addressed this issue, it is unclear if this is an intended reference or not.
 * According to Luffy, it was Shanks and the Red-Haired Pirates who taught him the song "Bink's Sake".
 * Luffy also claims that they need a musician because pirates sing. This is influenced by the Red-Haired Pirates, because he says that Shanks and his crew were always singing.
 * When Shanks and his crew appear in intros and outros, they are usually the last (or one of the last) of the important characters that have appeared in the series to be seen if the outro/intro features the previously seen major characters in the series. This is considering the crew are some of the first characters actually seen in the series and their captain was responsible for starting Luffy's adventure off by giving him his Straw Hat.
 * The ship of the Red Hair Pirates in One Piece seems to be based of the ship of Crescent-Moon Galley from Romance Dawn