Yesterday, my fourteen-year old boy turns to me and asks, “Mom, why is Mickey’s dog named after the Roman god of the underworld?” So, let’s review the early days, with a little help from the Disney Archives and Cartoon Shorts Club:
We see Pluto for the first time in the 1930 short, The Chain Gang. He doesn’t have a name, though. And he looks so little like the Pluto we know today, I’m just gonna have to take Disney’s word for it that this is the same character. Plus, he seems to have been twins. (And hey, there’s a short section right around 7:00 that reminds me of Trolly Troubles with Oswald the Lucky Rabbit.)
Watching The Chain Gang this morning made me wish even more that we could see old-school hard-times Mickey Mouse facing today’s economic troubles.
When we see him next in The Picnic, also released in 1930, his name is Rover. Plus, he’s Minnie’s dog, not Mickey’s, as my friend Eliyanna points out in an early episode of Those Darn Cats, A Room of Minnie’s Own.
When The Moose Hunt is released, the pup is now named Pluto, and belongs to Mickey.
The Disney Archives are silent on the reason for the name change. Wikipedia reports what is also widely speculated elsewhere:
Although it has been claimed that the Disney studio named the dog after the planet (rather than after the mythical god of the underworld), this has not been verified. Disney animator Ben Sharpsteen has said: “We thought the name [Rover] was too common, so we had to look for something else. […] We changed it to Pluto the Pup, […] but I don’t honestly remember why.”[9]
And, in turn, this then-newly-discovered (and now recently-demoted) planet had been named by an eleven-year-old girl in the UK. According to Wikipedia:
The name Pluto was proposed by Venetia Burney (1918–2009), an eleven-year-old schoolgirl in Oxford, England.[27]Venetia was interested in classical mythology as well as astronomy, and considered the name, that of the Roman god of the underworld, appropriate for such a presumably dark and cold world.
So there you have it, kid. The best I can tell you is that Mickey’s dog is named after the Roman god of the underworld? Because Venetia and Ben said so. But Eliyanna, I still don’t know why Mickey stole Minnie’s dog.
Broke Hoedown 
It definitely is interesting stuff, Jen – and that’s not all! According to the old Floyd Gottfredson comics, Pluto was simply a dog who started following Mickey around – and another story says that Mickey adopted him from a shelter and named him Pluto because he was passing by a newsstand selling newspapers with a cover story related to the planet Pluto. The beautiful thing here, in my opinion, is that each of us can just pick one theory to subscribe to.
-Carlo
Custodian from TDC #89
Carlo, you rock! Thanks for the added info.