It's interesting to see how many changes had Mickey Mouse before he became how he is now.

Early sketch of Mickey Mouse

Early look of Mickey Mouse

The early Mickey Mouse character was a bit naughty. It's also obvious in "Steamboat Willie". 

Even the pictures above of early him show the cheeky and naughty look. 

In latest animation Mickey became more naive with a positive attitude. The look is now more simple and polished.

One my favourite animation of Mickey "The pointer" (1939)