I’m a big fan of the Detective Thorne series of books by Mark Billingham. This author deliberately does not describe his protagonist’s physical appearance and is interested to hear the different mental images that readers have of him.

This exercise was a lot harder than I expected it to be. I have quite a clear picture of what I think the character looks like – serious, focused, with heavy features and dark curly hair – but haven’t managed to quite capture it on the page.

https://uk.markbillingham.com/tom-thorne/a-man-without-a-face