Darth Vader, born Anakin Skywalker, was a Dark Lord of the Sith and Military Executor in the service of Emperor Palpatine until his death at the Battle of Endor.
Anakin Skywalker, shortly after taking on the mantle of Darth Vader, was ordered by Palpatine (in order to increase the dark side's hold over him) to lead the 501st Legion of clone troopers into the Jedi Temple and kill every Jedi and Padawan inside. Vader did this without question, slaughtering venerable Jedi and younglings alike. Some of the Jedi children approached him, unaware that he was to be their destroyer. The atrocities made by Vader and the 501st Legion resounded in a smoke rising from the pillars easily visible from the Senate building. Palpatine then commanded Vader to travel to the planet Mustafar, where he was to kill the Separatist Council.
After Obi-Wan Kenobi informed Vader's wife, Padmé, of her husband's malefactions and sympathized with her, she went to Mustafar to try to reason with Vader, afraid for him and wanting to leave public life to live together and raise their child. When he heard this, Vader told Padmé that he could remove Palpatine as Emperor and that they could rule the Galaxy together, something that he would later repeat to their son, Luke. Padmé, shocked at this revelation, declined his offer, realizing that her husband was truly gone.
Vader and Obi-Wan fought an intense battle throughout the mining complex and down the river of lava outside. The battle ended on the banks of the lava river with Obi-Wan grievously maiming his former pupil.
Shortly after, the heat of the lava ignited Vader's clothing, burning his body severely. He was nearly immolated as he slid down to the edge of the burning river bank.As the flames started to subside, Vader kept himself alive with the Force and his unbreakable will, Vader clawed his way back up the bank with his still intact mechno-arm, all the while struggling with near-fatal third-degree burns and severe lung damage, not to mention emotional pain.
Darth Sidious arrived and found his apprentice spent of almost all his energy up slope from the lava river. He took him back to Coruscant and repaired the damage to his body through intensive cybernetic enhancement. He ordered the medical droids to keep him awake during the process so the pain would fuel his rage and therefore his power. His new robotic arms and legs were an updated version of the same technology that transformed Grievous into a cyborg.
As Darth Vader, Anakin became a powerful asset to the fledgling Empire, serving as an enforcer, Jedi hunter, Supreme Commander of the Imperial Fleet, and Executor of Palpatine's New Order.
During the Galactic Civil War shortly before the Battle of Yavin, Vader tracked the Death Star plans to a small Rebel outpost on Polis Massa. The 501st Legion stormed the facility, but failed to recover the plans. He was able to track where they were sent—Tantive IV, a corvette belonging to Princess Leia Organa of Alderaan.
Vader once more lost the plans, but gained a small victory by capturing the Princess. Utilizing an interrogation droid, he tortured Leia regarding the location of the secret Alliance base. At the same time, Vader ordered the execution of Owen and Beru Lars after the couple refused to give any details on the missing droids. Later during her captivity, Vader forced her to look on as Grand Moff Wilhuff Tarkin obliterated her homeworld during the destruction of the planet Alderaan. Vader also battled the elderly Obi-Wan Kenobi, his former mentor, in their second lightsaber duel. Despite Obi-Wan's vague warning that killing him would make him "more powerful than you can possibly imagine", Vader struck him down, and Obi-Wan became a spirit in the Force who continued to guide Luke Skywalker. To determine the location of the Rebel base, Vader allowed Luke and Han Solo to rescue Princess Leia and escape with the technical readouts of the Death Star.
During the Battle of Yavin, he almost prevented Luke's attack on the Death Star from being successful. Vader sensed that the young pilot in his sights was Force-sensitive, putting into motion a series of events that culminated in the death of the Empire. After the battle, Vader launched his personal mission to discover the identity of the one who destroyed the Death Star.
Vader believed that his unborn child had perished with his wife, Padmé Amidala but Vader eventually deduced that Luke was in fact this child. The Sith Lord became obsessed with hunting down Luke, an objective which neatly coincided with his task of destroying the Rebellion.
To deceive the Emperor, and thus allow him to continue making motions towards his own plan, Vader suggested that Luke could be turned to the dark side of the Force. The Emperor agreed, noting that Luke would be a "great asset". Meanwhile, as was the pattern with Sith Lords, particularly the Emperor, Palpatine also began planning to eliminate Vader and take Luke as his apprentice.
Vader asked Luke to join him so that they could destroy the Emperor and rule the Galaxy as father and son, harkening back to what he'd hoped to have with Luke's mother. Profoundly shaken by the news that he was Vader's son, Luke refused to join his father.
On Endor, Vader once again attempted to persuade Luke to join the dark side, but this time Vader's interests were tinged by a desire to protect his son. When this failed, Vader took him to Emperor Palpatine himself on the incomplete Death Star II. Luke reluctantly fought a lightsaber battle with Vader, all the while attempting to persuade his father into renouncing the dark side of the Force. During a lull in the fighting, Vader telepathically examined Luke's mind and discovered Leia Organa. Having figured out that his wife Padmé had twins just before she died, he correctly concludes that Luke and Leia were siblings. Vader threatened to turn her to the dark side if he should fail to do so with Luke.
Hearing this threat to his sister, Luke's rage was finally unleashed, and he attacked Lord Vader using the dark side of the Force, driving him back with a whirlwind of blows. Severing Vader's right hand, Luke's fury was suddenly cut short. Staring at his own cybernetic hand, Luke realized with a visceral horror that he had already begun transforming into Vader's successor.
As the Emperor approached, Luke threw down his lightsaber and refused to join the dark side. Palpatine, his hate for the Jedi resurging, struck Luke down with Force lightning.
Luke writhed and howled in agony as the Emperor slowly tortured him. He begged his father for help; Vader turned and, with his remaining hand, lifted the Emperor and threw him down a shaft into the Death Star's reactor core, where he exploded in a storm of dark energies. As Vader did this, he was hit with the full power of Palpatine's Force lightning, which shorted out his life support systems. In his final moments, he pleaded with Luke to remove his mask so that he could look on him with his own eyes. Vader found redemption in the light side of the Force. Darth Vader was no more; Anakin Skywalker, the Chosen One, had returned and brought balance to the Force by killing Palpatine and himself.
While Darth Vader may have been redeemed, he still left a dark legacy in the form of Dark Lady Lumiya. Upon his death and the death of Palpatine, Lumiya assumed the title of Dark Lady of the Sith and would eventually corrupt Vader's grandson, Jacen Solo. Thus, while Vader did fulfill the ancient Jedi prophecy, he allowed the Sith to rise once more, as per the prophecy of the Sith'ari.
