Severus Snape is revealed as the Half-Blood Prince in J.K. Rowling’s Harry Potter series.
The title is central to Harry Potter and the Half-Blood Prince, the sixth novel. Harry finds an old Potions textbook filled with handwritten notes and improvements attributed to the Half-Blood Prince, which makes him unusually successful in class.
The identity is eventually linked to Snape, who was the son of Tobias Snape, a Muggle, and Eileen Prince, a witch. “Half-Blood” describes his mixed magical and non-magical parentage, while “Prince” comes from his mother’s family name.
Snape is a complicated character: he teaches Potions and later Defense Against the Dark Arts, resents Harry because of Harry’s resemblance to James Potter, and has a long history involving Lily Potter and Dumbledore. His full motivations become clearer near the end of the series.