"Known to" means that someone or something is known to a specific group:
i.e. This snake is the deadliest one known to man!
**Here, the snake is one of the deadliest known to mankind (specific group)
"Known for" means that someone/something is recognized for some special trait or quality:
i.e. The chef is known for his delicious lobster.
**The chef is recognized by other people for his lobster (it is very delicious, which makes it a special feature)