The unofficial ruler of House Slytherin at Hogwarts, accepted by the Hydra Throne. Notable Princes of Slytherin have been Tom Riddle and Harry Potter. Less notable princes were Lucius Malfoy and Regulus Black.
Harry: I don’t want to be Prince of Slytherin (flailing like a wimp)
Hydra Throne: It has been decided. You are the newest Prince of Slytherin.