Most of the time the author tries to give a description of the protagonist or protagonists, but personally, when the description is not so specific, I like to imagine the characters with an actor or another fictional person, either to make it funnier or because of reading several works at the same time. I imagine something similar happens to others.
In my case, I remember that when I read Lisey's Story, I couldn't stop imagining Scott and Lisey as Kaneki and Touka from Tokyo Ghoul. I know, it was a bit weird, but it made my reading 10 times more enjoyable.
by Significant-Town-817