The Star Puppy is a legend that is explained in The Star Pup.
No one knows who the Star Puppy is, but according to the legend, the Star Puppy is apparently a descendant of the former rulers of Earth with a heart-shaped birthmark. If this Star Puppy is found, he will rid the forces of evil and bring peace.
The Legend of the Star Puppy
Long ago, the Pound Puppies' ancestors used to be the rulers of Earth. However, their peaceful lives are cut short when Slaughter and his tribe of barbarians drove the former rulers into a forest. The ancestors then found comfort when a group of pure-hearted humans, including Holly's ancestor, cared for them and saved them. In return, the Pound Puppies' ancestors granted these pure-hearted humans with Puppy Power and shared a secret that a descendant of these former dog rulers will defeat the forces of evil and bring peace to the world.
TriviaAt the end of The Star Pup, Cooler goes to sleep and leaves his back uncovered. Cooler's back has a heart-shaped birthmark, which may mean that Cooler is the real Star Puppy. However, this is never explained again for the remainder of the TV series.
This is a possibility on how Puppy Power was created.