Sad, that it is so empty here. Maybe the difficulty is the definition of when a philosopher can be considered underrated or under-read? How would one make that assessment? What barrier needs to be overcome to make a philosopher no longer underrated or even overrated?

Off the top of my head, I would propose most Greek philosophers, aside from the famous ones. But really any country has their history of philosophy.

Side note: I guess the most under-read philosophers are those whose works are no longer available to us and can thus no longer be read :c