Mickey Mouse made his big screen debut on November 18, 1928 in "Steamboat Willie", the first animation ever to use synchronized music and sound, and thus our love for Mickey Mouse began.
Mickey Mouse was actually featured in two cartoon shorts prior to "Steamboat Willie", they were "Plane Crazy" and "Gallopin' Gaucho" but those two films (which had no sound) were turned down by distributors and did not (originally) make it into theaters. After the immediate success of "Steamboat Willie", Walt Disney set the two previous films to music and sound and distributed the three together as a package.
It is interesting to note that after Universal Studios let Walt Disney go they hired Walter Lantz (who later created Woody Woodpecker) to oversee production of "Oswald the Lucky Rabbit" cartoons. Lantz went to Walt Disney to ask for tips in producing Oswald, Disney liked Walter Lantz and they became good friends. Also interesting to note is that in 2006, Disney traded sportscaster Al Michaels, who wanted to leave ABC (owned by Disney) and work with John Madden for NBC for the copyrights back to "Oswald the Lucky Rabbit". Disney reportedly has plans to put Oswald back into action.
For the kiddies - Go to coloring-book.info to find tons of fun Mickey Mouse coloring pages.
Sources: Wikipedia.org 1