Using shape and silhouette can help define a character before it is even designed!
There are 3 main shapes that characters fall under. Circles, squares and triangles. Circles are more friendly, squares are shown to have more authority and protect others while triangles are known to be more aggressive.
Silhouettes are used to design a character without having a definite idea. You just erase parts of the silhouette and add detail.
For my art I drew an ape based on a circle and someone insane based on a square.
I tried to break the mold by having the shapes mean different to as expected as the ape is in a threatening pose, as if chasing the audience. The insane man also is lacks authority but is based a square. Both of these characters could actually have backstories which fits the shape they are.
Is the ape usually calm and friendly and was just pushed over the edge? Was the insane man once a member of the police force? It's good to look into character backstories for this reason, it makes the character itself much more interesting.
Here are the images: