The clash on Mustafar, alternatively referenced as the battle that occurred on Mustafar, involved a lightsaber duel where Anakin Skywalker, who had recently become the apprenticed Sith Lord, Darth Vader, engaged in combat against his former Jedi Master and close confidant, Obi-Wan Kenobi. This confrontation transpired on the planet Mustafar, situated within the Outer Rim. Upon discovering Skywalker's descent alongside Grand Master Yoda at the Jedi Temple, Kenobi journeyed to Mustafar, aiming to reason with the fallen Jedi, as he doubted that the Sith Master known as Darth Sidious, revealed to be Emperor Palpatine, had entirely dominated Skywalker's will. Nevertheless, Vader had dismissed their friendship, swiftly declaring Kenobi as his adversary; subsequently, they activated their lightsabers and clashed, fighting amidst the carnage at the Klegger Corp Mining Facility, where Vader had just annihilated the members of the Separatist Council, the governing body of the Confederacy of Independent Systems.
The battle moved across the structures of the expansive facility suspended above Mustafar's lethal lava flows. Soon, Kenobi and Vader were stranded on a collection arm linked to the facility; the lava severed this arm from the main structure, causing it to descend into a fiery stream. Kenobi successfully landed on a lava skiff moving in the opposite direction. Vader pursued Kenobi, leaping onto a droid collector, where their fight went on. The Jedi jumped to a high lava bend, declaring the duel over because of his elevated position. The Sith Lord tried to follow, but in his arrogance, Vader failed to defend against Kenobi's final strike, a powerful blow that severed Vader's remaining organic limbs, causing him to tumble to the lava bend's edge, ending the duel.
Afterward, Kenobi—filled with disgust and sorrow for his friend's transformation—lamented that he had believed the fallen Jedi was the Chosen One destined to destroy the Sith, but instead, he had joined them. Unable, or unwilling, to aid his former friend, Vader was engulfed by the lava's flames that spilled onto the bend; Kenobi left the Sith Lord to die, taking his fallen apprentice's lightsaber as he retreated. Later, Vader's new master, Darth Sidious, discovered his injured apprentice and transported him back to Coruscant, the galactic capital, now known as Imperial Center, for reconstruction; the suit Vader then wore became his permanent attire as a Dark Lord of the Sith.
During the period of conflict known as the Clone Wars, a trio of Jedi—Obi-Wan Kenobi, Anakin Skywalker, and Ahsoka Tano—were taken to Mortis, a unique realm, by its resident Force wielders. These beings held the belief that Skywalker was the prophesied Chosen One, destined to bring balance to the Force and eliminate the Sith. One of these beings, the Son—representing the dark side of the Force—revealed a vision to Skywalker. This vision showcased events from his future, including the Jedi Knight's transformation into Darth Vader, a Dark Lord of the Sith, who would contribute to the Jedi's destruction and the Sith's galactic dominance. The vision briefly led Skywalker to embrace the dark side, but he rejected it, and the Father erased his memory of the future.
The duel's origins trace back to Darth Sidious, the Sith Master who, as the newly appointed Galactic Emperor Sheev Palpatine, tasked Skywalker, now the fallen Jedi and his new apprentice Darth Vader, with the assassination of the leaders of the Confederacy of Independent Systems on the volcanic Outer Rim planet Mustafar, aiming to conclude the Clone Wars. Vader arrived on Mustafar with R2-D2 aboard his Actis-class interceptor, and was followed by his wife, Senator Padmé Amidala. There, he revealed his plans to seize control of the Empire, proposing to overthrow Emperor Palpatine and rule the galaxy together. However, the senator refused, expressing disbelief in his actions. Upon seeing Obi-Wan Kenobi, his former Jedi Master, Vader, mistakenly believing Amidala had led him to Mustafar to kill him after learning Obi-Wan was right about Vader, used the Force to choke her.
Obi-Wan persuaded Vader to release Amidala and, reluctant to kill his former Padawan, initially attempted to reason with Anakin. When it was clear that his former student would not listen, Obi-Wan reluctantly drew his lightsaber, prompting Vader to do the same.
The lightsaber battle between Kenobi and Vader was extensive and fierce, without a clear advantage for either combatant, as their skills were evenly matched; their years of partnership allowed them to anticipate each other's moves, effectively reading each other's minds. Ultimately, Kenobi summoned all his strength to overcome his former Padawan.
The duel unfolded across the Klegger Corp Mining Facility, with the two adversaries fighting through hallways, conference rooms, and command centers. Their misdirected weapons inadvertently triggered a meltdown of the facility when they struck a control panel. Consequently, the facility's shielding deactivated, and the large stalks overhanging the lava river collapsed under erupting lava, one of which carried the two combatants along with it.
Kenobi and Vader continued their fight on the collection arm as it drifted down a lava river. Upon reaching a lava fall, Kenobi jumped onto one of the mining platforms floating above the river. Believing Vader dead, he discovered the Sith Lord perched on a lava mining droid, having leapt from the structure before its destruction. As their battle continued, they floated back upriver, exchanging verbal insults. Kenobi desperately tried to reach out to Skywalker, attempting to convince him of Palpatine's evil, but when Vader insisted the Jedi were evil, Kenobi declared his former student and friend beyond redemption.
The battle moved back upriver before concluding on a nearby embankment where Obi-Wan jumped, securing the high ground. He pleaded with Vader not to attack, but Vader, consumed by anger, refused and attacked, only to have his left arm and both legs severed.
Following Kenobi's passionate condemnation of Vader, who was believed to be the Chosen One destined to destroy the Sith instead of joining them, Vader's body ignited in flames from the intense heat of the lava river, burning him alive. Unwilling to kill his defenseless enemy, Kenobi took Vader's lightsaber and regretfully left him on the embankment, presumed dead, before departing the planet with the dying Amidala. Kenobi believed his former Padawan had succumbed to his injuries and died, a belief shared by R2-D2.
Sidious sensed his apprentice's distress across the galaxy and traveled to Mustafar to rescue him. Unknown to Kenobi or R2-D2, Vader had barely survived, dragging himself from the lava bank before Sidious found him. The newly crowned Emperor transported Vader back to Coruscant, where he placed his severely wounded apprentice into a cybernetic suit that would sustain him for the remainder of his life. Only then did Vader learn he had killed his wife in anger.
Meanwhile, Kenobi brought Amidala to Polis Massa, where she died shortly after giving birth to her and Anakin's twin children, Luke and Leia. To protect them from the Sith, the twins were separated. Senator Bail Organa adopted Leia, while Kenobi delivered Luke to his former apprentice's stepbrother, Owen Lars, and his wife, Beru, on Tatooine. Vader later established his personal fortress on Mustafar, largely due to its significance in his rebirth as a Sith Lord.
To safeguard Luke, Kenobi went into exile on Tatooine, adopting the alias Ben Kenobi. He became aware of the Inquisitorius, a group of corrupted Jedi assisting the Empire in hunting down survivors of Order 66. However, Kenobi remained unaware of Vader's survival until ten years after their duel. When Organa requested his aid in saving Leia on Daiyu, Kenobi discovered that the kidnapping of Leia Organa had been orchestrated by the Inquisitor known as the Third Sister, who hoped to bring him before Vader to gain the Sith Lord's favor. Kenobi was shocked to learn Vader had survived, and could only mutter Skywalker's first name as he escaped Daiyu with Leia. Later, when Kenobi and Organa traveled to the mining world of Mapuzo, Vader arrived with the Inquisitors and Imperial Army to finally have his long-awaited rematch with his former mentor.
Vader won the duel but chose to torture Kenobi instead of killing him, burning him before he was rescued by members of the Hidden Path. After Kenobi's wounds healed and Vader failed to capture him during the attack on Jabiim, they engaged in another duel on a barren moon, which Kenobi won. When the injured Vader declared that he had destroyed Anakin Skywalker, Kenobi bid farewell to the Sith Lord, believing that the man he had considered a brother was truly gone. Afterward, Organa returned home to Alderaan, where Kenobi told her he knew her birth parents but referred to them in the past tense. On Mustafar, Sidious made Vader declare that his former Jedi Master meant nothing to him to ensure his apprentice could overcome his past, but Vader still yearned to find Kenobi again.
The final encounter between Kenobi and Vader occurred on the first Death Star during the Galactic Civil War during a mission to rescue Princess Organa. Kenobi warned the Dark Lord that he could not win, and striking him down would only make him more powerful. Vader angled his blade upwards, declaring that Kenobi should never have returned from exile. Kenobi glanced into the hangar, where he saw Skywalker. He turned to Vader, smiled wryly, and raised his lightsaber. Vader slashed at Kenobi, but he had vanished, having become one with the Force.
During the Battle of Endor, Anakin achieved redemption, inspired by his son Luke, sacrificing himself to kill Sidious before rejoining Kenobi and Yoda in the Force as a spirit. Between 4 ABY and 5 ABY, Skywalker's Force spirit appeared on Mustafar to rescue those trapped in his former castle. The crew left Vader's servant Vaneé, who thought he was hearing the voice of his fallen master due to Mustarian lava fumes, trapped in the castle, hallucinating Vader coming for him.
The possibility of a confrontation between Obi-Wan and Vader was first suggested in the original 1977 film Star Wars: Episode IV A New Hope. Hints of a duel are present in the original trilogy, such as the conversation between Kenobi and Vader on the Death Star, Vader's scars, Obi-wan's comments about Vader being more machine than man, and Vader's remarks about Obi-wan once thinking like Luke. The concept dates back to at least 1977, when George Lucas told Rolling Stone magazine in an interview that "Vader kills Luke's father, then Ben and Vader have a confrontation, just like they have in Star Wars, and Ben almost kills Vader. As a matter of fact, he falls into a volcanic pit and gets fried and is one destroyed being."
The official novelization for Return of the Jedi includes passages where Obi-wan tells Luke that Anakin fell into a pit of lava, clawing his way back out as Darth Vader. It also includes a moment where Vader remembers the feeling of molten lava crawling up his back, and he equates Luke's unconditional love as pulling him back from that pit. Reference materials produced after the original trilogy, such as 1994's Star Wars Screen Entertainment and 1997's The Galactic Empire Scrapbook, also alluded to the pair dueling alongside a "volcano" with Obi-Wan being able to "back Anakin into an open pit of molten lava." These versions of the events were reworked and later retconned by the prequel trilogy when the lava-filled duel between Obi-Wan and Vader appeared in the 2005 film Star Wars: Episode III Revenge of the Sith. By then, it had become a highly anticipated event in Star Wars fandom.
George Lucas spent nearly two weeks completing the duel, which only occupied half a page in the script. During the animatics stage, Steven Spielberg, Lucas' friend and a renowned Hollywood filmmaker, contributed to the duel's production. Ewan McGregor and Hayden Christensen, who portrayed Obi-Wan and Anakin, practiced the duel for months. The speed of the duel in the completed film reflects the actual filming speed, without digital acceleration. Lucas named the duel during an interview in the documentary Within a Minute: The Making of Episode III.
In the DVD commentary of Episode III, George Lucas noted that during the scene where Vader chokes Obi-Wan, the latter is holding the former's lightsaber. Obi-Wan was originally intended to take Vader's blade, and shots were filmed but removed from the final cut for pacing.
As shown in The Making of Star Wars Revenge of the Sith, concept art by Sang Jun Lee depicts Kenobi and Skywalker originally fighting a creature known as the Mustafar Monster during the duel. This idea was scrapped in the finished film. Additionally, Vader was meant to beg Kenobi for help, reaching out to him, but Kenobi, while acknowledging his love and initial inclination to help, refuses, with Anakin's eyes turning from blue to the trademark yellow of the Sith.
Before the duel, Vader tells Kenobi, "If you are not with me, then you are my enemy!" Kenobi responds with "Only a Sith deals in absolutes." George Lucas intended this line to reflect his perception of viewers' opinions on US President George W. Bush's "War on Terror," particularly Bush's "black-and-white" worldview.