Snape was a dreaded character for quite some time for all Harry Potter readers. His reputation was murky because of his past as a death eater and he was constantly stalking Harry and his friends. Slowly it began to dawn upon us that he couldn't be entirely evil. It was only in the end, [SPOILER ALERT] after Nagini had dealt Snape the death blow that Harry came to know all about him. Our hearts raced fast as we saw Snape tell Dumbledore how he had always loved Lily.
Harry was not kidding when he told his son that he was named after one of the bravest men he had known. And his love for Lily gave him the strength to fight Voldemort while standing with him. Here is a clip that shows Snape's chronological journey through the Harry Potter world.
Source - kcawesome13