Who are "the Trio"?
Harry Ron Hermione
Who tells Harry he is a wizard?
Who is the headmaster of Hogwarts in books 1-6?
Who is Harry's aunt, who is his uncle, and who is his cousin?
Petunia Dursley, Vernon Dursley, Dudley Dursley
Who is Harry's nemesis?
Lord Voldemort/Tom Marvolo Riddle
Who is the headmaster of Hogwarts in book 7, and why?
Severus Snape, because,
A. He killed Dumbledore