The Jazz Singer.
Showed the potential of sound in cinema.
Disney, Steamboat Willie, Silly Symphonies and the 1939 Snow White and the Seven Dwarfs. Not only the leading forces in sound synchronisation but the first to realise the potential of colour presentations and realistic animation of human proportions. A lot of early Disney were game changers in and of themselves. Using expensive but new film processes. Like Fantasia was the first to use to use stereophonic techniques that are still used and even inspire innovations to this day.
And many works that proceeded them, they utilised new and experimental techniques, to various degrees of success, arguably pioneering various cinematic techniques.
Say what you like about Walt, he was in the end a true visionary.