Severus Snape in the Harry Potter series seemed so evil, only a few
thought he was a good guy the whole time. I despised him throughout the series of the books, and I never thought he would turn out to be the biggest hero in the end.
The Biggest Twist in Harry Potter and the Deathly Hollows
At the end of the book, Snape dies a tragic death and when Harry just learns Snape was loyal to Dumbledore to the end. Mostly everyone thought he was a death eater and hated him, but he remained unloved until the very end.
Dumbledore's Sanity
Many people thought Albus Dumbledore was mental to trust Snape and even Harry Potter questioned Dumbledore's wisdom. Dumbledore was always right, but when Snape killed him at the tower, I was sure Dumbledore was proved wrong once and for all. Dumbledore turned out to be right as always.
Evilness of Snape
J.K. Rowling pretty much exaggerated how evil Snape was in every book. Very few people guessed he was really loyal to Dumbledore the whole time.