Known to...or known by

Harry Potter is known by everyone.
Harry Potter is known to everyone.

I have my own idea but the reference book has given the opposite answer, which of course is not unusual.

I think it’s “to”.
“by” is used, but it might be incorrect. Off the top of my head, “by” is used to replace “beside/next to” and to show method.

it seems natural to me that people are known to people and facts are known by people.

I’d go with either one here.

“known by” is a simple function of the past participle of “know” which is used in forming the passive voice. People know him. He is known by people.

“known to” is a common phrasal verb. John is known to the police.

My feeling is that “known by” connotes a more personal connection than “known to”. Contrast “John is known to the police” and “John is known by the police.”

The latter would generally be written as, “The police know John.” So, using “known by” is a matter of style. If it can be rewritten in active voice it would probably make for stronger prose.

“known to” and “known by” also have different meanings, in which case you would have to choose the appropriate one:

“known to”= have the reputation for doing something
“known by”= be able to be recognized using some means

I second Tempo Gain’s opinion. Very well put, Tempo. So in the Harry Potter sentence, it should be “known to”.