Halley is Colonel Sassacre's dog. Halley's dog house is destroyed by a meteor carrying a baby Grandpa. After Grandpa accidentally shoots and kills Sassacre, Halley acts as the guardian of both Grandpa and Nanna, though Grandpa often says the name incorrectly as Harley due to an odd speech impediment. Years later Grandpa rides Halley off as he goes off on an adventure.
On Halley's first appearance it was noted that he bears a striking resemblance to Bec, Jade's Guardian. Despite the resemblance, he appears like an ordinary dog and has none of Bec's reality-warping abilities. It was later shown that Halley was used to clone Bec by the Draconian Dignitary using Rose's journals. Andrew stated that Bec is not completely omniscient like some first guardians because of Halley being his genetic source, confirming that Halley himself is just a normal dog.
Halley shares his name with a comet.