Walt Disney was the one who conceived The Haunted Mansion, originally aimed at being a walk-through ghost attraction. Walt would oversee many of the choices made for the mansion but didn't want a dilapidated building mucking up the beautiful scenery of Magnolia Park. Instead, a visit to the Winchester Mystery House in San Jose served as inspiration for the mansion.
Production on the Haunted Mansion attraction was delayed several times due to Walt's involvement in the 1964-65 Worlds Fair. Walt Disney died in 1966, three years before Disneyland's Haunted Mansion would open.
Marc Davis was responsible for the animatronics of the Hat Box ghost while Yale Gracey worked on the effects.
Walt Disney was set to appear in audio-form in the queue for one draft of the Haunted Mansion penned by Ken Anderson.
Walt and his brother Roy, cameo in a photograph of Mystic Manor opening in 1908. Admittedly impossible. Walt Disney would have been seven years-old during the time period the photograph was taken.
Growing up in Los Angeles in the 70s/80s we visited Disneyland on a regular basis and often after school, before "Annual Passes".