Can you name a philosopher whose first name is Karl, and isn't Karl Marx or Karl Jasper?

I have to do a report on a philospher named "Karl" but I don't remember his first name. I think it might have started with "Rho-"


It's definately not Karl Marx or Karl Jasper.


Thank you!

Can you name a philosopher whose first name is Karl, and isn't Karl Marx or Karl Jasper?
Karl Raimund Popper?