Darth Vader returns to the Jedi?

Question

What were the reasons that Darth Vader, from Return of the Jedi, turned away from the Darkside in the end?

Answer 1

Anakin Skywalker was a powerful Jedi during the Clone Wars. But against the wishes of Jedi Order, and in secret, he married Padme Amidala, and she became pregnant with twins (though neither knew they were twins at the time). Anakin began to have dreams of Padme dying in childbirth, and combined with the fact that he was unable to save his mother from dying at the hands of the Sand People, worried about losing Padme. Thus, it was simple for

Chancellor Palpatine, who was really the Sith lord Darth Sidious,

to seduce Anakin to the dark side by promising the power to save Padme from dying. Of course, this way he became Darth Vader. However, once Padme saw that Anakin had turned, she was broken-hearted

and lost the will to live, dying after giving birth to Luke and Leia.

However, Darth Sidious told Vader after he awoke from surgery that he (Vader) killed her in his rage, thus cementing his fall to the dark side.

Of course, he didn't know that Luke and Leia had been born. Flash forward 19 years, and the Emperor Palpatine has found out that Luke is the offspring of Anakin Skywalker. Vader makes it his mission to hunt him down, ostensibly to turn him to the dark side as well. It is speculated that Palpatine wanted a "whole" apprentice to replace Vader, and Vader wanted an apprentice so that he could challenge his master.

However, there must have been some distrust of Sidious at that point when he realized that Sidious had lied all those years ago about Padme's death.

Then, after trying to lure Luke to the dark side in his encounter on cloud city, revealing that

I am your father

They met again on board the second Death Star at the battle over Endor, Luke constantly trying to turn Anakin back. They dueled in front of the Emperor, and after Vader's taunts about possibly turning Leia to the dark side enraged Luke, Luke sliced off Vader's hand, defeating him. Sidious, cackling with triumph, urged Luke to kill Vader and become his apprentice. Vader then saw that he had been betrayed, and slowly rose to his feet when Luke refused to turn to the dark side. Sidious then savagely attacked Luke with force lightning, inflicting terrible pain. Luke called out for help, crying Father, please.

Wookieepedia notes:

As Vader watched Sidious savagely torture Luke, his love for his son--one of the few parts of Anakin that was still left--finally bloomed in full after being reawakened four years earlier. It was enough to finally break the dark side's hold over him. From that moment on, Darth Vader was no more, and Anakin Skywalker was reborn.

Anakin picked up the emperor, throwing him down a shaft of the Death Star, killing him. Unfortunately, enough lightning struck Anakin to inflict mortal wounds. Luke tried to save Anakin, but Anakin said that Luke was right about him - that there was still good in him. With that, Anakin died and became one with the force.

TL; DR: So in short, he turned back because he realized Sidious was merely using him, and had betrayed him and out of love for his long-lost son.