Orochimaru, one of the Legendary Sannin, yet a vile monster, mostly a snake-like person, twisted and mindless, he is the definition of pure evil and the ones who follow.He was one of the main villains of Naruto until he meets his end by Sasuke Uchiha.
Sarutobi considered Orochimaru a genius seen once only in a couple decades and tried to groom him to be Hokage, but Sarutobi watched Orochimaru's heart become blacker after his parents' murder and started to favor Jiraiya. After the 4th Hokage's death, Sarutobi discovered Orochimaru's atrocious crimes, kidnapping and experimenting on the villagers to create new jutsus. Sarutobi couldn't bring himself to kill his student, allowing Orochimaru to escape. Jiraiya pursued him, but he too couldn't kill his friend.
Orochimaru joined a group called Akatsuki, but did not share their interests, he was only interested in Itachi. When he couldn't take Itachi, he left the organization and took his ring with him. He then formed his own ninja village in the Land of Rice, tempting the warlord with power but secretly wanted to use the village as a giant lab. This village is called Otogakure, also called the Sound village.
Orochimaru first appeared during the Chuunin exams forest of Death exam. He sent three Sound ninja ( Dosu Kinuta, Zaku and Kin) to kill Sasuke. But, Orochimaru had other plans for Sasuke and disguised himself as a grass ninja and went looking for Sasuke himself. Team seven had an extremely hard time with Orochimaru, as he was so much stronger than they were. Sasuke had planned to just give the mysterious man their scroll instead of continuosly losing to him. It was then that's Narutos fist crashed straight into Sasuke's face. Orochimaru told them that Naruto had a point, because if he really wanted to take their scroll that he'd just kill them. Orochimaru then summoned an enormous snake to fight them, and Kyuubi had to stop it. Sasuke was so surprised to see Naruto do something so valiantly (and with such strength) that it gave him a short burst of courage and let him face Orochimaru head-on without fear. Sadly, Sasuke's newfound courage could not bend reality and Orochimaru defeated him. He left them, but not before biting Sasuke in the neck and branding him with a mysterious seal. He would later encounter Anko, a former student of his that he left behind. She had issues with Orochimaru, she slammed him against a tree and, while holding one of his hands, stabbed both her hand and his to pin it against the tree. She was about to use a suicide technique to kill both herself and Orochimaru, but it would turn out that it was a Shadow Clone and the real Orochimaru had amused himself watching them fight. He told her that he had his eye on a "successor," and asked her not to sto pthe exam. Orochimaru would then infiltrate the chuunin exams disguised as the Sand village's Kazekage and sat next to Sarutobi.
When the Sand and Sound villages attacked the Leaf village, Orochimaru kidnapped Sarutobi and took him to a special location. He revealed himself to Sarutobi and told him that he was the leader of the Sound village. He had four of his Sound ninjas create a barrier around the battlefield and attacked Sarutobi. The fight was very brief before Orochimaru decided to toy with Sarutobi by resurrecting The First Hokage and The Second Hokage as his mindless attack dogs. Sarutobi was forced to fight his deceased mentors with Orochimaru watching in sadistic pleasure. At one point in the battle, Orochimaru would start mocking Sarutobi on how not even the "God of Shinobi" could defeat age, and that's when Orochimaru pulled off his "face" to reveal that of a young woman; Sarutobi realized that he has achieved immortality by stealing the bodies of others. Orochimaru would join back into the battle, but Sarutobi, realizing the odds against him, used "Reaper Death Seal" in an attempt to seal away his opponents' souls. However, Orochimaru stabbed Sarutobi through the chest in an attempt to save his life but Sarutobi was able to seal Orochimaru's arms. With the battle over, Orochimaru left.
Orochimaru would have his medical assistant, Kabuto, attempt to cure him and even find doctors that could help, but nothing did. Orochimaru decided it was time to find Tsunade, his former teammate. He promised to revive her loved ones in return for healing his arms and said that he'd return for her answer. She met with him but Kabuto interrupted, knowing the technique she was going to use would kill Orochimaru. The two fled to a more suitable fighting ground with Tsunade in pursuit. Jiraiya, Naruto, and Shizune arrived to aid Tsunade.
Orochimaru personally fought Jiraiya, but while Orochimaru couldn't use his arms or techniques that required hand seals, Jiraiya was drugged by Tsunade and was having a hard time moving and controlling his chakra, making the short fight somewhat even. Orochimaru attacked, but Jiraiya defended himself with Needle Guardian. However he couldn't use the technique as well as he wanted and Orochimaru, despite impaling his foot on Jiraiya's needle-like hair, managed to bite deeply into Jiraiya's neck. The two released their hold and had an argument. Orochimaru surprised Jiraiya by suddenly going after Naruto and managed to slam Jiraiya hard into the ground. Orochimaru pulled Kusanagi out of his mouth and was about to kill Naruto, but Tsunade saved Naruto. Tsunade was impaled and Orochimaru was shocked, but Tsunade used her "Creation Rebirth" technique to heal her otherwise fatal wound and gave Orochimaru a savage beating, forcing him and Kabuto to escape.
Later, Orochimaru would send The Sound Five: Tayuya, Jirobo, Kidomaru, and Sakon & Ukon to sneak into the Leaf village to give Sasuke an invitation. But they took too long and Orochimaru sent Kimimaro to help. Though all five would die, Sasuke found his way to Orochimaru.
Orochimaru and Kabuto had a plan to ambush Sasori and kill him when he came to meet Kabuto, whom he thought was his spy, but were surprised to find themselves being tricked by Team 7. The situation quickly escalated into a fight between Orochimaru and and Naruto. Orochimaru taunted Naruto and Naruto, starting to sprout tails, swiped at Orochimaru's face and tore off his "Vanishing Facial Copy," but Orochimaru fixed it.
Orochimaru taunted Naruto again, making Naruto sprout more tails and ripped off Orochimaru's arm, but Orochimaru pealed off his skin to expose a perfectly healthy body underneath, complete with arm. Orochimaru started taunting Naruto again as he sprouted a 4th tail, Orochimaru spat out many snakes from his mouth, each holding a knife in their mouths, but Naruto destroyed them. Orochimaru tried to stop Naruto with a snake extending from his sleeve, but it too was destroyed and Orochimaru was sliced in half at the waist, but dozens of snakes extended from the two halves and pulled himself back together. Naruto began to gather chakra into a large ball, worrying Orochimaru who then summoned three "Rashoumon" gates to protect himself, but they were destroyed by the resulting blast. When the dust settled, Orochimaru wasn't there, instead surprising Naruto by sprinng up from beneath Naruto trying to stab him with the Kusanagi, but it didn't work. Feeling his body was failing him, Orochimaru escaped while Yamato tried to subdue Naruto.
Before he left, he was encountered by Sai who had business to attend to on the behalf of Danzo. Orochimaru stabbed Sai with the Kusanagi, saying that it's impolite not to talk to someone in person, to which the "Sai" that Orochimaru stabbed was revealed to be an Ink Clone. The real Sai appeared and offered him a deal which Orochimaru accepted and brought Sai with him and Kabuto back to his lair. Much later after Team 7 arrived to retrieve Sasuke, Orochimaru stopped Sasuke from trying to kill them, saying that they are killing Akatsuki for them, and thus they're useful. They then all left.
Orochimaru's technique was wearing off, the body was rejecting him more and more and he needed to transfer himself into Sasuke. Sasuke barged into Orochimaru's room and pinned him to the wall. He said that Orochimaru is weak and there was nothing more he could teach him, but Orochimaru mocked him, calling him a left-over Uchiha. Sasuke was about to strike the death blow when Orochimaru turns into his true form, a white snake made up of hundreds of smaller white snakes. Orochimaru has a flashback of when he was young, standing at his parent's grave with Sarutobi. Orochimaru found the shedded skin of a snake and he asked what it was. Sarutobi told him that it was the shedded skin of a very rare white snake and that they symbolized good fortune and rebirth, and that him finding it near his parents' graves maybe means that they have been reincarnated and that he'll see them again one day. Orochimaru asked when, but Sarutobi told him he didn't know the answer to that. Orochimaru held the skin, smiling. Back to the fight, all the snakes on Orochimaru's "body" are attacking simultaneously. Sasuke defended himself against the attacks and taunted Orochimaru as he activated his level two Curse Seal and then slices Orochimaru in three halves, but starts to feel sick. Orochimaru's severed head taunts Sasuke, saying that his snakes have poisoned the air. Orochimaru then yells out "I am undying!" as he lunges to take Sasuke's body, Sasuke is then shocked to find both of them in something of a dimension that Orochimaru controlled. Sasuke began to be consumed by the strange organic-like material within that world. Orochimaru has another flashback to when he tried to take Itachi's body, Itachi placed Orochimaru in a genjutsu and when Orochimaru tried to perform a technique, Itachi cut off his hand, telling him that all of his techniques are useless against the Sharingan. Back to the present, Sasuke put Orochimaru in a genjutsu and the strange material that was consuming Sasuke instead began to consume Orochimaru... absorbing Orochimaru with his own technique. Kabuto found Orochimaru's remnants and grafted some of Orochimaru onto himself to gain his power, however he has discovered that Orochimaru is trying to take control and he's trying to resist.
In Sasuke's battle with Itachi, Itachi used his third Mangekyou Sharingan technique called "Susanoo," which takes the form of a giant humanoid. Orochimaru starts to whisper in the weakened
Sasuke's head, telling him that he can help Sasuke exact his revenge, telling him to release his power. A white snake appears from Sasuke's shoulder and he transforms into a giant multi-headed snake, this is Orochimaru's "Yamata" technique. He attacks Itachi, but Susanoo forms a sword and strikes him down. Orochimaru emerges from the multi-headed snake and is excited, claiming that the moment he was waiting for has come. He has broken free of Sasuke and will take his body, however he is once more struck by Susanoo's sword. Orochimaru laughed, saying that such an attack couldn't kill him... but then he recognized the sword, it was a sword he had been searching for called Totsuka no Tsurugi, a sword that has sealing properties which traps the victim in an eternal genjutsu. Orochimaru and the snakes coming from Sasuke's body are then pulled into a jar Susanoo was holding. Zetsu mentioned that it was no wonder Orochimaru couldn't find it, it didn't have a physical form. Itachi then makes his way to Sasuke who's on the ground.
As Susanoo finishes absorbing Orochimaru from Sasuke, one of the white snakes escapes and slithers into the rubble.
In one of Naruto's recent flashbacks of his training with Jiraiya, Jiraiya stated that Orochimaru started acting strange after his parents deaths, somewhat similar to Sasuke. It should also be noted that once Orochimaru had been confronted by Itachi years before, he had been defeated in a gen jutsu battle, and his first thoughts were standing with Sarutobi at his parent's graves, where he was given a speech by his former sensei on how the white snake sheds its skin to become more beautiful and redeeming than it was before, symbolizing rebirth.