It's the "Thinker" by Rodin.
Different casts by the same artist from the same molds.
The cast in Cleveland is in front of the Art Museum, and was hit by a bomb by domestic terrorists in 1970. The original is in Paris. An undamaged cast in Denmark is here: http://en.wikipedia.org/wiki/The_Thinker
the damaged Clevaland one here: http://www.case.edu/alumni/stay/wsched.html