Suigetsu is from the Hidden Mist village and was being trained by Zabuza to be one of the Seven Swordsmen. He now wields Zabuza's sword.
After Sasuke defeated Orochimaru, he went to what appeared to be a water tank. After he released the water in it, the water formed into Suigetsu. Sasuke then persuaded him to be a part of the new team he planned to form wich would be called team Hebi. Suigetsu was told of Sasuke's intentions to recruit Karin and Juugo, which Suigetsu replied that he wouldn't get along well with them. Sasuke told him that they didn't have to get along, just work with each other. After some words, Suigetsu made it clear that he didn't like Sasuke's acting like the boss and that him beating Orochimaru doesn't mean anything to him and that sooner or later someone of them was going to take him down. He then threatened Sasuke, but smirked and said that he was just joking. Knowing that Sasuke helped defeat Zabuza and Haku, he had Sasuke take him to where team 7 buried Zabuza's and Haku's corpses, in order to take Zabua's sempai sword by saying that the swords of the Seven Swordsmen of the Mist are passed to the successor...
The two then go to one of Orochimaru's hideouts to recruit Karin, a dedicated follower of Orochimaru's who's skilled in sensing chakra and is infatuated with Sasuke. Suigetsu and Karin have an instant dislike of one another; Suigetsu doesn't trust her and thinks she's skittish, apparently he cought Karin doing soemthing to Sasuke wich is yet to be revealed. Also Karin wants to be alone with Sasuke and dislikes Suigetsu's "jokes." While there, Suigetsu releases all of Orochimaru's victims, but when he goes back to see if Karin agreed to join them, he's surprised to find that the door is locked and cuts it down, angering Karin who was trying to put the moves on Sasuke. He then goes with Sasuke and Karin to recruit Juugo from another of Orochimaru's hideouts. Suigetsu advised against bringing Juugo with them, knowing of his homicidal mood swings, and Suigetsu actually had to fight Juugo briefly after releasing him but Sasuke stopped the fight and Juugo agreed to go with them, believing Sasuke has the power to stop him if he can't stop himself.
During Sasuke's battle with Deidara, he was searching for Kakuzu's banker in order to gain some information regarding akatsuki but he couldnt get nothing important. Sasuke summoned Manda and unsummoned him while inside his mouth to escape Deidara's enormous explosion. Suigetsu had a summoning scroll and some of Sasuke's blood that he used to summon Manda and Sasuke back. Just recently Team Hebi has caught up with Itachi and Kisame. When they found them Kisame told Sasuke to go on ahead alone, and that he would watch the other three. Sasuke did so. After Itachi left, Suigetsu asked Kisame if he remembered him. At first Kisame didn't see it, but then realized Suigetsu was the younger brother of Mangetsu Hozuki (wich died during a mission with Suigetsu). Suigetsu then offered that them and Kisame "kill some time" while waiting for Sasuke and Itachi.
Later, Suigetsu is accompanying Team Hebi, now called Team Taka, along with Tobi and Kisame. Sasuke wants to kill Konoha's village elders, but Kisame says that they will be protected and his team isn't powerful enough. Suigetsu is insulted by this and says that Zetsu stopped their fight before he could get serious and attacked Kisame, but Tobi stopped Suigetsu. Sasuke said that Suigetsu isn't powerful enough yet to defeat Kisame. Kisame smirked at that statement and Suigetsu told Sasuke that they'll be eating shark fin soup one day.
Then Team Taka went to fight the Eight Tailed Beast. Suigetsu went first, but Killerbee [the Eight Tailed Beast's jinchuriki] easily blocked his sword. Then he, Juugo and Sasuke tried to attack Killerbee all together, but again Killerbee beat them all. Then Suigetsu was thrown into the water, watching as Killerbee transformed into the Eight Tailed Beast. He then controlled a certain amount of water to try and protect his teammates from the Eight Tailed Beast's attack. The result was that he was hit at full force, leaving him in a semi-water form. After they manage to capture Killerbee, he is later seen asking his teammates why they left his sword behind, receiving an angry answer from Karin. He is then surprised to hear that Sasuke might not want the Beast's power to destroy Konoha.
When leaving Akatsuki, Madara appeared and said they had a deal and can't leave until they uphold that deal, turns out Killer Bee tricked them, so Madara sent them on another assignment: kill Danzo at the Kage summit, which Sasuke was eager to do. They went to the Land of Iron where the summit was taking place, they were going to wait for Danzo to leave before attacking him, however Zetsu appeared and told the Kages that Sasuke was there. Raikage and his bodyguards, Darui and Shii, found Sasuke and attacked. Shii used a genjutsu and Sasuke was almost killed by Raikage and Darui, however he was saved by Juugo and Suigetsu. Juugo went CS2 and tried to fight the Raikage and Suigetsu got into a swordfight with Darui, while Sasuke defeated Shii. Juugo was beaten by Raikage and Sasuke attacked, but he too was nearly killed and and Darui's lightning jutsu rendered Suigetsu's watery body paralyzed. Gaara appeared and saved Sasuke from Raikage and tried to talk sense into him, but he failed and Sasuke managed to escape. Suigetsu and Juugo left soon after during the confusion.
Suigetsu hasn't shown much. So far it's seen that he's composed of water and hitting him has no effect, seeing as the attack will just go through him; and become a huge tidal wave. He also has the ability to temporarily increase the size of his muscles, adding to his strength. Furthermore, he can "control" water, and use it like a shield, to protect his teammates, for example.