Mickey Mouse's original name was Mortimer Mouse

Mortimer's name was originally meant for Mickey Mouse but Walt Disney's wife Lillian thought the original name made Mickey seem pompous. Years later, the name was used for a new character created to be a rival for Mickey.

Mortimer only appeared in the cartoon "Mickey's Rival" and was never seen again until the late 90s early 2000s when Mortimer's popularity skyrocketed and landed him roles in several Mickey Mouse related material.