What is the name of the Jetsons' dog?

The name of the Jetsons' dog is Astro.

Astro is the Jetson family's large, talking Great Dane and one of the most recognizable characters in the Hanna-Barbera series. He lives with George, Jane, Judy, and Elroy in the Skypad Apartments in Orbit City, alongside the family's robot maid, Rosie.

Astro is famous for beginning many words with an “R” sound, produced as part of his growling speech pattern. That vocal gag is often compared with Scooby-Doo's distinctive speech, although Astro is a separate character and was voiced primarily by Don Messick in the original television series.

A common mix-up is confusing Astro with Orbitty. Orbitty is the family's later alien pet, while Astro is the dog. Astro also did not appear in the earliest title sequence as prominently as some other characters, but he became central to the show's family comedy and later specials and films.