way way back, i think hitchcock used it in the one where cary grant dragged that woman up the presidents face, Charade? North by North West? can't remember.
Petro Vlahos (the creator of Chroma-key or, as it was known, Color Traveling Matte Composite Cinematography) won a Scientific Award at the 1964 Oscars for the use of his technology which helped make possible the combination of live action with animated actors in the film Mary Poppins.
The parent trap (1961) was a ground-breaking film featuring the virtually unheard use of split screen - featuring the teo Hayley Mills' as twins. they used a small ammount of live action and cartoon together but as both Parent Trap and Mary Poppins were Disney filmsthat's to be expected and they expanded the live action and cartoon in Mary Poppins