* Walt Disney's birth: Walt Disney was born on December 5, 1901.
* The Walt Disney Company's founding: The Walt Disney Company was founded in 1923 by Walt Disney and his brother Roy Disney.
* First animated short film: Walt Disney's first animated short film, "Alice in Cartoonland," was released in 1923.
* First Mickey Mouse cartoon: Mickey Mouse made his first appearance in the short film "Steamboat Willie" on November 18, 1928.
So, the answer to your question depends on which aspect of Disney you're interested in.