During the first wizarding war, Gellert Grindelwald was defeated by Marvolo Slytherin instead, or he was once known as Tom Riddle, in stead of Dumbledore. The news that said that a dark lord was defeated by a dark lord has got Albus Dumbledore trigger in anger, but he can't do anything about it since Marvolo has now move on to be the Minister of the wizarding world, and also the hero inside the witch and wizard eyes. He still has one last hope, the Potter.