In my opinion, it's the 5 Wizards that was sent from Valar to Middle-Earth, Olorin, Curumu all of them, before they took the name of Gandalf and Saruman, OH WAIT! You're talking about Harry Potter wise, my mistake.
Well I believe that would have to be the 4 founders of Hogwarts, Helga Hufflepuff, Rowena Ravenclaw, Godric Gryffindor, and Salazar Slytherin...