When it was disclosed in Harry Potter and the Deathly Hallows back in 2007 that Snape was truly the double agent and had done everything for his love, Lily Evans, the readers went crazy. Here, the cruel Slytherin Potions Professor was shown a more loving side. When we had first received knowledge about Snape's part in Lily's life as seen in the Order of Phoenix and the Half-Blood Prince, Snape was someone that Lily cared for seeing as he was a good friend of hers, but after he showed his true side by telling her that she was a "Mudblood", she finally realized what her friends had been telling her all along, he was like them all, the same cruel Dark Arts loving Slytherin. While at this time many others also saw James Potter for the boy he had been at this time, a bully, he was always portrayed as a hero and here we saw him as what Snape became later in his life. But then in the Half-Blood Prince, we found out that it was he who had told Lord Voldemort about the prophecy, it was he who had doomed the Potters and the Longbottoms to death, but ultimately Voldemort decided that it was the Potters. We showed resentment towards him, anything that we may have shown towards James Potter and his bully techniques was nothing compared to this. Being the sly snake he was he listened to Trelawney's prophesy and went off to his master to spill the news. This is what we had known of Snape, but then J.K. Rowling drops the massive dung bomb explosion, we learned that he had truly loved Lily Evans and he as once as he had realized his mistake he rushed off to Dumbledore to plead his allegiance to save Lily. We realized that he had done everything to help keep Harry alive all these years, many, many people forgave Snape for all of his doings, seeing him as a hero. In fact to help with this, a little before this was dropped onto us, it was revealed that he was the one who told Lily that she was a witch and once they entered the train we saw the beginning of James Potter, the bully. People exploded with emotions, believing that he was a hero.
Now the real question is, was Snape a hero?
No, a hero- is a person or character in literature who, in the face of danger and adversity or from a position of weakness, displays courage or self-sacrifice—that is, heroism—for some greater good. This was penance for what he did to the woman that he had loved. He was responsible for her and her husband's death as well as a orphaned child.
Many people will argue and say how he risked his neck for Harry, but really, isn't this what any Professor at a school with high dangers should do. Yes, he became a double agent, but who was he a double agent for, no not Dumbledore, but Lily, it was his fault that she was targeted and his fault that she was murdered.
Well then why would he stay a double agent after her death? Well there are many reasons, Dumbledore could have as easily exploited this secret and Snape could have been done for, he also asked Dumbledore what could he do, he needed to punish himself for the crime that he had committed.
There are still many people that would disagree, lets take a look at this "hero"
We have no proof that Remus ever actively bullied Snape, he was likely a passive bystander. It had been years since they had seen each other, Remus had turned over a new leaf, he treated Snape as an equal, his fellow Professor. What did Snape do, he could not let go petty things that happened when they were teenagers that Remus didn't even do. It was known that when they were in school, Snape tried to exploit Remus for what he was, 15 years ago and couldn't let go of a part of Remus' happiness after many years of not having a dash of sunlight, he ended this by exploiting him at breakfast in the Prisoner of Azkaban.
He constantly bullied his student do you understand, this is someone that he was supposed to care for, he bullied him so much that Neville's worst fear was Snape. Don't try and tell me that this was Voldemort could have chosen Neville instead of Harry and Lily could have been alive, NO. That is all Snape's fault, he cannot blame a child for his crime. Has Neville not suffered enough? His parents are mentally insane, his former renowned Auror parents were driven insane because Voldemort's plan did not work out, he could not successfully kill Harry, so his most sadistic Death Eaters went and destroyed that family.
There are far too many reasons that show Snape as a anti-hero.
He didn't even do this for Lily, it was for himself, it was his penance. If he had actually done it for Lily then he would have put aside his petty rivalry with the Potters and would have cared for Harry like many of the other Professors did, who were not tasked with protecting him. So no, he didn't protect harry for Lily, he did it because he needed to do something to wash away the guilt of his crimes.
And all of you who saw that it was rumoured that Lily was pregnant with another child and wanted Snape to be the godfather and for James to forgive Snape. Please, just stop it, you're making me throw up. He was a Death Eater, no one knew of his alliance, why would a Member of the Order of Phoenix, enemy of Death Eaters, tell her husband to disregard Snape? Honestly, she ended a toxic relationship with his years ago.
And those "I want someone to love me how Snape loved Lily" things. So you want them to basically organize your murder and spent the next years harassing your child? Well then, I guess your wishes are your wishes
But in the end, it's your choice, was he a hero?