The Akatsuki symbol.
Akatsuki (暁, Literally meaning: "Dawn" or "Daybreak") is a criminal organization comprised of S-rank Missing-nin and is the most wanted group in the shinobi world.
Akatsuki first appeared in the Rock Lee Springtime of Youth Jumpfest Special. They were shown meeting up under a giant balloon version of Naruto.
Akatsuki members Deidara and Tobi made two attempts to infiltrate the Leaf Village, both of which ended in humiliating defeat thanks to Lee, Neji, and Tenten.
In chapter 16, the entire organization of Akatsuki was meeting up and Lee and Tenten managed to infiltrate the meeting under the guise of being a new recruit. Lee and Tenten managed to escape after accidentally causing a massive riot between the members, destroying the cave as Tobi and Zetsu arrived. In the anime episode version of events, Deidara tried to help them escape to avoid them revealing how he was humiliated. Tobi accidentally blabs that Deidara knew Lee/Tenten was a spy, causing the entire group to beat him up.
In the Rock Lee Springtime of Youth Special Collaboration Chapter, Pain, Kisame, Deidara, Tobi, and Kakuzu attempted to steal a copy of "Naruto SD Powerful Shippuden" from Naruto and Lee. Pain, Deidara, and Kisame, play Lee and Naruto in a game of Smash and Shield Rock-Paper-Scissors with Tobi as referee but lose. They end up forcing Kakuzu to buy copies of the game for the members.
In chapter 21, Kisame ended up unknowingly getting stuck back to back with Might Guy thanks to a gorilla's sticky chakra. Itachi worked with Neji, Tenten, and Lee to find them while Kisame and Guy worked together to defeat the gorilla. The gorilla gets lose again at the end of the chapter and Itachi and Kisame end up stuck together.
In episode 47, Kisame brings Samehada to a dog cafe and has him pretend to be a dog that ends up befriending Akamaru. Tobi ultimatey shows up and gets Kisame kicked out by revealing Samehada wasn't really a dog.
In episode 51, Akatsuki teams up with Sasuke to destroy the Leaf Village. Itachi is implied to have died sometime before this episode. Kakuzu, Konan, and Pain are shown fighting Ino, Shikamaru, and Choji. Kakuzu and Konan are later shown captured.
In chapter 27 of the manga, the entire Akatsuki organization went on a summer vacation because Pain believed it could bestow unbelievable power. At the end, they started to have a competition to see whose sparkler can last the longest. The Akatsuki decided to have a different kind of sparkler competition with their jutsu, destroying the beach. Pain and the rest of Akatsuki noticed their skin had become darker and believed it was a sign of them becoming more powerful like Pain intended. They actually just got sunburned.
Akatsuki members have a very distinctive wardrobe, which could give them away if a village is alerted of their presence. Members wear long, dark cloaks with red clouds, a red interior, and a chin-high collar. Members also wear nail polish and rings on specific fingers of their hands.
Though Akatsuki is made of the shinobi worlds most dangerous criminals, they are often defeated in humiliating ways. Their evil plans often range from destroying the Leaf Village to stealing a video game. There have even been occasions were they actually helped the good guys. Akatsuki members usually don't get along and constantly fight amongst each other. Pain acts as the leader of the organization and Kakuzu acts as the treasurer. Akatsuki members are organized in teams of two.
Akatsuki teams are put together in teams of two to exploit combined strengths for the organisation's goals to be met.
Hidan and Kakuzu have shown the most hostility towards each other due to a conflict of interest; Kakuzu saw the rituals and beliefs of Hidan's religion to be a waste of time, while Hidan saw Kakuzu's willingness to do blasphaemous things and his greediness to be unbearable, not to mention that Kakuzu's job as a bounty hunter usually got on Hidan's nerves. As a result of their sideline in collecting bounties and conducting rituals, this team was usually late in the line of work.
As leader of Akatsuki, Pain directed the rest of the organisation to their respective goals, while Konan serves Pain as his second-in-command.
Formed by the two artists of Akatsuki, Sasori and Deidara worked well for the most part but had conflicting ideas on art: Sasori believed in art forever preserved like his puppet while Deidara sees it to be instantaneous and gone in a flash like his Explosive Clay.
Posing as a happy-go-lucky idiot, Tobi was introduced as Deidara's second partner. Tobi's childish attitude is seen as an annoyance to Deidara's expectations of the organisation.
Not much is known about the duo in the spinoff, however, in the Naruto series, unlike most Akatsuki teams, Itachi and Kisame got along pretty well.
Technically not a "two-man team", the single being has two split personalities. On the right, the black half talks in a deep voice, while the left half has pale skin and talks normally.