Dolores Umbridge may have climbed to the top of mount hatred when it came to the villains of the Harry Potter Universe, but the two main enemies that the boy who lived had to deal with were Lord Voldemort and Severus Snape.
One is a sociopathic cult of personality who waged wars, had his servants commit murder en masse, and believes killing Harry is the key to a never-ending reign of dominance over the entire world. The other is a teacher. Severus Snape is a despicable, cold and cruel man who takes every opportunity to berate Harry.
Considering the intricate plan of Severus feigning allegiance towards the Dark Lord, he has had to get as deep inside the mind of Voldemort as anyone ever has in order to keep his deception intact. As such, the two happen to come off as fairly similar. After all, Severus is essentially the right-hand man of He-Who-Must-Not-Be-Named.
Do you think you can decipher which quotes came from Snape and which from Voldemort?