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He held the rank of Jedi, but the Jedi Council were jealous and didn’t give Anakin what he deserved.
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He saw visions of his wife dying and was willing to do anything to save her, yes, including killing kids. This isn’t evil; this is true love.
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After he became Vader, he found out his wife died.
Justifiable crash-out, to be honest


Also, he was the one who killed his wife.
Upon finding out that he was the one ultimately responsible, he went “nooooo” and I suppose went “well, as long as I’m in this cool suit, guess I’ll just keep doing the evil then”.
Frankly, I find his arc to be one of the least convincing “how a guy went evil and was redeemed” in fiction. Empire strikes back had the benefit of being able to leave it vague enough to leave it a potentially interesting turn, but when they actually had to delve into it, was pretty unfulfilling
Fun space action movies, but execution on the “twists” was not the strong point.