It's hard to believe now, but when Club Penguin launched, there were no puffles at all. At that time, the community of Club Penguin asked if they could have some kind of pet to adopt for their igloo, and they decided that, instead of using animals that already existed, they wanted to make up a completely new creature for the penguins to adopt.
Some of the ideas were combined, and the puffle as we know it now was born (although I liked the propeller one enough that they gave the green puffle a propeller cap to fly around with). I'd love to know what your very favorite thing is about puffles.