Lost in an archives near the frigid Arctic Circle was a 1927, early Disney Christmas cartoon film, Empty Socks. The film stars Oswald, the Lucky Rabbit, a Disney character that came before Steamboat Willy, otherwise known as Mickey Mouse. It has been found and was written up in The Guardian. Read the story here.
Steamboat Willie was first seen in 1928, and Mickey Mouse's appearance and demeanor has changed greatly over the years.
Look for the DVD, Walt Disney's Vintage Mickey [DVD WAL] to see several Mickey Mouse cartoons that were released between 1928 and 1934. Learn more about Mickey in the book Mickey Mouse from Walt Disney Productions [741.5 WAL], which has "Eleven adventures of Mickey Mouse and his friends in comic strip form and a brief discussion of Mickey's evolution from an animated film character to the official host for Disneyland and Walt Disney World."