While he's never been officially classified as a specific breed, he likely draws inspiration from the beagle due to its:
* Brown and white coat: Underdog has a similar color pattern.
* Stubby legs and floppy ears: These physical traits are common in beagles.
* Friendly and energetic personality: Underdog embodies these characteristics, even though he is a fictional superhero.
Ultimately, Underdog's breed is up to your imagination!