Harry Potter and the Goblet of Fire
How we cite our quotes:
At the moment, Harry fully understood for the first time why people said Dumbledore was the only wizard Voldemort had ever truly feared. The look upon Dumbledore's face as he stared down at the unconscious form of Mad-Eye Moody was more terrible than Harry could have ever imagined. There was no benign smile on Dumbledore's face, no twinkle in the eyes behind the spectacles. There was cold fury in every line of the ancient face; a sense of power radiated from Dumbledore as though he were giving off burning heat. (35.89)
As Harry grows older (especially in Harry Potter and the Half-Blood Prince), he begins to see another side of Professor Dumbledore. Professor Dumbledore seems like an absolute model of wizarding virtue and awesomeness in the first several books – a perfect mentor for Harry. But, as the books continue, we see a darker, more human side to Professor Dumbledore too. We learn that even he can make mistakes (what??). Harry's glimpse of Professor Dumbledore's cold rage in this novel sets the stage for many more discoveries later on in the series.