In Animation
He appeared frequently from 1930 to 1932 and less frequently afterward, making his final classic-era bow in 1942. The name of Horace's voice actor in the classic era is unknown.
Horace biggest role was in "Camping Out" in 1934, where he was pretty much the star of that cartoon.
In his earliest incarnation, Horace was presented as Mickey Mouse's four-legged plow horse. He could walk upright on his hind legs, at which time his forelegs became gloved hands; at other times, he got back down on all fours and reverted to form. Horace mostly played bit-parts in the approximately 30 cartoon shorts in which he appeared and his character was never as fully developed as the "Fab Five". Like Goofy in his early Dippy Dawg appearances, Horace's body seemed to be formed of rubber tubing. He and Clarabelle Cow had an uncanny ability to change from somewhat normal farmyard animals into anthropomorphized beings as necessary.
As with most Disney characters, he was given small cameos in Mickey's Christmas Carol (1983) and Who Framed Roger Rabbit (1988). He had a bigger role as the Prince's (Mickey's royal double) stone-faced tutor in the The Prince and the Pauper (1990).
In his latter-day animated appearances, his voice is provided by Bill Farmer (who also voices Goofy and Pluto). In the series House of Mouse, Horace plays a small role in some episodes as the club's technician, playing episodes of cartoons for the audiences and generally running the machinery.
After departing the Disney studio, Ub Iwerks created a Horace-like character, the mule Orace, for his own studio. As can be noted, even the name is almost the same.
In the 1990s, Horace was intended to star in a new TV series to be created for The Disney Afternoon, titled Maximum Horsepower, intended to explain his disappearance from the shorts after the 1930s ended. The concept would be that, in 1939, Horace had gotten tired of playing bit parts and, after learning Mickey was starring in Fantasia, was going to demand Walt to give him a starring role in that movie as well. On his way to Walt's office, though, he gets abducted by aliens who bring him halfway across the galaxy because they are in desperate need of the hero that they believe Horace is, despite his dreams of returning to Earth and resuming his acting career. Maximum Horsepower, however, never came to be.
Read more about this topic: Horace Horsecollar