I am still confused. DIdn't he do bad stuff... so did he start to become a villain? or was it always Dumbledore's plan?
Most Helpful Guy
Snape started as villain and became a good guy. Or rather, started as a good guy, became a villain, and went back to a good guy.
He was in love with Lilly Potter at school, turned to Voldemort after he lost her to James who had bullied him, then turned double agent for Dumbledore after Voldemort killed Lilly.
Dumbledore had tasked him with spying on Voldemort, and when Harry came to Hogwarts he also tasked Snape with protecting Harry.
Regarding what he did to Dumbledore, Dumbledore was already dying from the curse of the horcrux. They knew that Malfoy had been sent by Volodemort to kill Dumbledore, so Dumbledore made Snape swear to kill him instead for two reasons. First, he thought Malfoy could still be saved and turned away from the path of Voldemort. Second, he knew that if Snape did the deed instead of Malfoy it would put all of Voldemort's distrust about Snape to rest and make him his most trusted lieutenant so Dumbledore could discover Voldemort's full plans. So that was Dumbledore's plan all along. Snape didn't want to do it, but Dumbledore held his love for Lilly over his head and pressured him into it. So it was very much Dumbledore's intent the entire time.0