Star Wars Episode III: Revenge of the Sith

During a space battle over the planet Coruscant, Jedi Knights Obi-Wan Kenobi and Anakin Skywalker lead a mission to rescue the kidnapped Supreme Chancellor Palpatine from Separatist commander General Grievous. After infiltrating Grievous's flagship, the Jedi battle the Sith Lord Count Dooku. Anakin subdues Dooku and, on Palpatine's urging, kills him. Grievous flees the battle-torn cruiser, which the Jedi crash-land on Coruscant. There, Anakin reunites with his wife, PadmÃ© Amidala, who reveals she is pregnant. While initially excited, Anakin begins to have prophetic visions of PadmÃ© dying in childbirth, and his worry steadily grows.
Palpatine appoints Anakin to the Jedi Council as his representative, but the Council refuses to grant Anakin the rank of Jedi Master and orders him to spy on Palpatine, which diminishes Anakin's faith in the Jedi. Palpatine tantalizes Anakin with secret knowledge of the dark side of the Force, including the power to save his loved ones from dying. Meanwhile, Obi-Wan is dispatched to the planet Utapau to deal with General Grievous, and Yoda is dispatched to Kashyyyk to defend the planet from invasion.
Tempting Anakin, Palpatine eventually reveals that he is the Sith Lord Darth Sidious, saying that only he has the knowledge to save PadmÃ© from dying. Anakin reports Palpatine's treachery to Mace Windu, who confronts and subdues the Sith Lord. Fearing that he will lose PadmÃ©, Anakin intervenes on Palpatine's behalf, allowing Palpatine to kill Windu. Anakin pledges himself to Palpatine, who dubs him Darth Vader.
Palpatine issues an order for the clone troopers to kill their Jedi commanders and dispatches Vader and a legion of clones to kill everyone in the Jedi Temple. Vader massacres the remaining Separatist leaders hiding on the volcanic planet Mustafar, while Palpatine addresses the Senate, transforming the Republic into the Galactic Empire and declaring himself Emperor. Having survived the attack, Obi-Wan and Yoda return to Coruscant and uncover Anakin's treachery.
Unable to convince PadmÃ© about Anakin's turn to the dark side, Obi-Wan stows aboard her ship. PadmÃ© travels to Mustafar and implores Vader to leave the dark side. Vader refuses, and when he witnesses Obi-Wan, he chokes PadmÃ© into unconsciousness. Obi-Wan duels and defeats Vader, leaving him for dead on the bank of a lava flow. On Coruscant, Yoda fights Palpatine; their duel reaches a stalemate and Yoda flees. Palpatine, sensing that his apprentice is in danger, travels to Mustafar.
On the asteroid Polis Massa, Obi-Wan regroups with Yoda and PadmÃ© gives birth to twins, Luke and Leia, as she dies. A funeral is held for PadmÃ© on Naboo. On Mustafar, Palpatine finds Vader badly burnt but alive. After returning to Coruscant, he rebuilds Vader's mutilated body and outfits him in a black armored suit. Palpatine tells Vader that he killed PadmÃ© in his anger. Meanwhile, Obi-Wan and Yoda decide to hide the twins from the Sith, as they were the only hope to the galaxy for freedom. Yoda exiles himself to the planet Dagobah, while Vader and the Emperor oversee the construction of a massive space station, the Death Star. Bail Organa adopts Leia as his own daughter and takes her to Alderaan, while Obi-Wan delivers Luke to his step-family Owen and Beru Lars on Tatooine, where Obi-Wan intends to watch over Luke until the time is right to challenge the Empire.

Question: Who Defeats Vader?
Answer: Obi-Wan.