Severus Snape is revealed as the Half-Blood Prince in J.K. Rowling’s sixth Harry Potter novel.
The title Harry Potter and the Half-Blood Prince comes from notes written in an old Potions textbook. Harry uses the book’s annotations to excel in class, unaware that its former owner was Snape. Near the end of the novel, Snape identifies himself as the Half-Blood Prince.
Snape’s name reflects his parentage: his mother, Eileen Prince, was a witch, while his father, Tobias Snape, was a Muggle. “Half-Blood” describes a wizard or witch with both magical and non-magical ancestry, while “Prince” comes from his mother’s family name.
Snape is the Potions professor for much of the series and later becomes Hogwarts headmaster. His loyalties and motives are clarified further in Harry Potter and the Deathly Hallows, making him one of Rowling’s most morally complex characters.