Voting rights in parts of America before the Voting Rights Act depended on passing an arbitrary test that differed from jurisdiction to jurisdiction and may or may not have measured literacy and civics knowledge… if you were black (or native American, depending on state). You could be a well-regarded English literature professor at a black college and still have to subject yourself to what you knew was a farce being administered by someone far less literate than you in order to attempt to vote.
If you were white (“your grandfather could vote”), you were usually exempt, even if you could barely sign your name on your voter registration.