Harry Potter's archenemy, Voldemort, is also referred to as 'He who must not be named' and 'You-Know-Who' in the Harry Potter series.

Voldemort, the leader of the 'Death Eaters' main quest is to rid the wizarding world of Muggle (non-magical) heritage, and conquer both the wizarding world and Muggle world. Voldemort is the last descendant of wizard Salazar Slytherin, one of the four founders of Hogwarts School of Witchcraft and Wizardry.