* Proper nouns are specific names for people, places, or things. They are always capitalized.
* Koala is the common name for a specific type of marsupial. It's not a unique name.
* Bear is a general term for a large, furry mammal. It's not a specific name.
While you might hear someone say "Koala Bear," it's not grammatically correct. The proper way to refer to the animal is simply "Koala."