What is ratchet from ratchet and clank?

Its bugging me! at first i thought he was a cat and then some sort of cheetah thing but now i don't even know? could anyone tell me? oh! and if you know what to do after you blow up all the big spaceships on planet battle? the Plumber gave me some sort of thing that helps you find bolts in the ground and i don't know what to do? thanks!