"You showed exceptional courage, Harry. That was his one most prized quality in his students. Harry, what color of sparks did your wand shoot out when it chose you?" Dumbledore asked.
"Red, and gold."
"The exact colors of Gryffindor house..." The headmaster muttered, and seemed to be lost in thought. He took out his wand, and added a few more thoughts to the pensieve.
"Er, Professor?" Harry asked. "About the emerald knight...who are they, and why is Voldemort so worried about their return?"
Dumbledore seemed to be considering whether or not to tell Harry.
"Well, Harry..." He began. "When Godric Gryffindor began his wanderings of the world before he co-founded Hogwarts, he befriended the Ancient Egyptians."
Harry gave a start. Dumbledore was still staring at the desk, however, and appeared not to have noticed.
"Now...Godric was very fond of druidism. I assume you have studied the subject in class?"
Harry nodded.
"Godric, being very kind, taught the Egyptians all he could know about this particular topic. They were very eager to learn from him, and even built a series of study pyramids in his honour.
One day, while the Egyptians were muddling around underground, they detected a magical force of incredible proportions. They alerted Godric at once. Of course, Godric was immediate in his reaction, and went to the place of detection as soon as he was told."
"And what did he find?" Harry asked, an increasing sense of apprehension creeping down his spine.
"He found a book on a pedestal, labelled the Book of the Dead."
Harry's throat felt like someone was squeezing it.
"Whatever you may think, Harry...magic cannot bring the dead back to life," Dumbledore said. "No, Muggles love to dabble in those sorts of things. What happened was that as soon as Godric touched the book, it disappeared, and a suit of armour took its place.
Godric's curiosity, of course, demanded that he try it on, and Godric did. At once, he sensed incredible power flowing throughout him, and the mysterious knowledge that the suit would answer to whatever he asked. Worried that he would be corrupted in this power, Godric asked the suit to only answer to his heir, and sealed the chamber with several powerful magical spells."