So it was farewell Oswald and hello Mickey as Walt came up with a fresh character with the help of his oldest friend, animator Ub Iwerks.
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His wife Lillian was most unimpressed by the moniker and urged him to change it to Mickey.
Walt obliged, Mickey was born and the rest is history.
Reflecting on Mickey's A-creation, Walt once said the mouse appeared in his A-imagination in 1928 when "disaster seemed right around the corner" and he feared losing everything.
Other sketches now seen for the first time include a classic still from 1931 cartoon Fishin' Around -- where a sheriff finds Mickey defying an angling ban.
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Another sketch shows Mickey at a concert hall curtain in the 1936 classic Mickey's Grand Opera -- also featuring Donald Duck, Clara Cluck and Pluto.
One from the animation Mickey's Amateurs shows him with yellow hands.
Mickey was aged nine by then and had long been a superstar.