What is the name of Mickey Mouse's dog?

Mickey Mouse's dog is Pluto.

Pluto began as one of two unnamed bloodhounds pursuing Mickey in the 1930 cartoon The Chain Gang. He appeared next as Minnie's dog, Rover, in The Picnic, before becoming Mickey's pet and receiving the name Pluto in The Moose Hunt in 1931. This makes Pluto's identity as Mickey's dog a long-established part of Disney continuity.

Unlike Goofy, who is an anthropomorphic character capable of speaking and behaving like a person, Pluto is generally portrayed as a non-speaking, ordinary dog with expressive reactions. That distinction is a frequent source of confusion, especially because both characters are associated with Mickey Mouse. Pluto later became popular enough to headline his own theatrical shorts, beginning with Pluto's Quin-puplets in 1937, and appeared in dozens of Disney films, comics, television programs, and games.