Herpo the Foul is one of the overarching antagonists in J.K. Rowling's Harry Potter and Fantastic Beasts and Where to Find Them series. He was a Dark Wizard and pioneer from Ancient Greece who was said to be one of the most powerful and influential users of dark magic. He is infamously known for being the first to create Horcruxes, the most terrible and evil dark magic in the Wizarding World, as well as the Basilisks, one of the most feared dark creatures.
Biography
Little is known about Herpo the Foul's past, but he was born with the ability to speak Parseltongue, the ability to communicate with snakes. Herpo was a very powerful but evil wizard who invented the darkest and vilest forms of magic curses. He was also notoriously known for creating the first Basilisk during his many experimentations.
Having strong knowledge on the nature of the soul and how murder affects it, Herpo has deliberately (but ruthlessly) committed murder to split his soul and seal it away in a relic that would come to be known as the first of all Horcruxes. His contributions of dark magic has an eternal impact on the Wizarding World and the act of creating a Horcrux is regarded as the darkest form of magic, and possibly the only one that is considered purely evil magic.
Being born to speak Parseltongue, this makes Herpo one of the earliest known Parselmouths. He might have been an ancestor of Salazar Slytherin because of his ability to speak to snakes.
It's unknown how/if he died and who destroyed his Horcruxes if he was indeed killed. Some Harry Potter fans think that his Horcruxes were destroyed by the venom of his own Basilisk, as it is one of the few things that can destroy a Horcrux. Other don't even know if he died due to lack of information on him. In case of his death, it's not known if he was send to a eternal crippled state in Limbo forever like in the case of Lord Voldemort or if he was allowed to move on as Voldemort's case could have been an exception as he created more Horcruxes than anyone and never showed remorse for his actions, though it's still unknown how many Horcruxes Herpo created nor if he ever felt remorse for his actions.
Legacy
Herpo the Foul's reputation of creating the basilisk and Horcruxes would strongly influence Tom Marvolo Riddle/Lord Voldemort to use the Basilisk of Salazar Slytherin to purge Hogwarts of all muggle-borns and create several horcruxes to become immortal.
